Device and method for characterizing the stiffness of a vehicle suspension mount

Abstract

The invention relates to a device for characterizing the stiffness of a suspension mount of a motor vehicle, comprising: - a central part (10) having substantially three orthogonal planes of symmetry (XY, XZ, YZ) and comprising at least two flat zones (Z11, Z12) respectively parallel to the first two of said planes of symmetry, and - two end parts (20) extending on either side of the central part (10) and comprising means for centering and maintaining two mounts in a symmetrical position with respect to a third of said planes of symmetry. Figure for the abstract: Fig. 1

Description

Title of the invention: Device and method for characterizing the stiffness of a suspension mount of a motor vehicle Technical field of the invention

[0001] The present invention relates generally to motor vehicle suspensions.

[0002] It relates more particularly to a device and a method for characterizing the stiffness of a suspension mount of a motor vehicle. State of the art

[0003] A motor vehicle generally includes, at each of its wheels, a suspension system essential to ensure a comfortable and safe driving of that vehicle.

[0004] Various suspension systems are known.

[0005] For example, it is known to use strut systems that are interposed between the vehicle chassis and the wheel carriers (which support the wheels).

[0006] Such a strut generally includes a jack for stress damping, and a spring threaded around the jack.

[0007] The upper end of the spring rests against a cup commonly called a "stop". This stop carries, on the side opposite the spring, a pad generally made of elastomer.

[0008] The strut is thus fixed to the vehicle chassis by means of this block which is sandwiched between the stop and the chassis and is thus adapted to filter vibrations.

[0009] This stud can be found in other suspension systems.

[0010] In all these systems, this block makes it possible in particular to filter the rolling noise generated by the road surface, and more specifically by its granularity, before it reaches the chassis.

[0011] These rolling noises have a frequency between 50 and 300 Hz.

[0012] The effectiveness of filtering these frequencies will depend directly on the stiffness of this pad, which stiffness can be modified by playing both on the material used to manufacture the pad and on the shape of this pad.

[0013] Unfortunately, it proves difficult to develop these blocks, in particular because it is difficult to measure this stiffness, due to the particular shape of this block and its position on the strut.

[0014] It is understood that in order to carry out these measurements, it is necessary to apply a preload to the block, corresponding to a quarter of the weight of the car if it has four wheels, then to apply a vibratory excitation along an axis distinct from the preload, while making measurements, which proves complicated when seeking to obtain accurate and reliable results directly on the vehicle or on a test bench. Presentation of the invention

[0015] In this context, the present invention proposes a device for characterizing the stiffness of a suspension mount of a motor vehicle, comprising: - a central part which has substantially three orthogonal planes of symmetry and which includes at least one flat area parallel to one of said planes of symmetry, and - two end parts which extend on either side of the central part and which include means for centering and maintaining two pads in a symmetrical position with respect to another of said planes of symmetry.

[0016] Thus, the invention proposes a modal analysis measurement device which includes a central part of adapted mass and which accommodates not one single stud, but two studs in symmetrical positions.

[0017] This device is thus designed to facilitate the implementation of the characterization of the stiffness of each block, both during the installation of the device in a measuring bench and during the measurements themselves.

[0018] Other advantageous and non-limiting features of the device according to the invention, taken individually or in all technically possible combinations, are as follows: - the central part has a parallelepiped shape, with six faces, one of which bears the said flat area; - the central part has a cubic shape; - each flat area extends to the center of one of the faces of the central part; - each end part has a rotational symmetry around an axis; - each end part has a variable diameter, which is maximum at its junction with the central part; - each end part has, at a free end, a threaded part; - said centering and holding means comprise a suspension stop engaged on each end part, and a nut screwed onto each threaded part so as to lock said suspension stop; - each flat area is at least partially surrounded by a protruding relief; - at least two flat areas are planned, respectively parallel to two of the said planes of symmetry; - the central part and the two end parts form a single-piece body shaped in such a way that the rigid body modes and the elastic deformation modes of said body are respectively located in distinct frequency bands.

[0019] The invention also proposes a method for characterizing the stiffness of a block by modal analysis, in which the following steps are provided: - locking two pads in a symmetrical position on a device such as the one described above, - locking the two blocks into a fixed frame, - application of an excitation to one and then the other of the two flat areas, - vibration measurement of the device, and - determination of the stiffness of each pad based on the vibration measurements taken.

[0020] Of course, the various features, variants, and embodiments of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. Detailed description of the invention

[0021] The following description with regard to the attached drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be carried out.

[0022] On the attached drawings:

[0023] [Fig-1] is a schematic perspective view of the body of a device characterization according to the invention;

[0024] [Fig.2] is a schematic perspective view of the entire characterization device of the [Fig.1];

[0025] [Fig.3] is a schematic perspective view of the characterization device of the [Fig.2] accommodating two pads and installed in a measuring bench;

[0026] [Fig.4] is a graph illustrating the variations in the vibration amplitudes of the body of [Fig.1], expressed in dB, as a function of their frequencies, expressed in Hertz, for three orthogonal directions.

[0027] A motor vehicle comprises a chassis and wheels. It also generally comprises a suspension system at each of its wheels, which allows the chassis to be mounted in a suspended manner relative to the wheels.

[0028] Each of these suspension systems is attached, on one side, to the wheel and, on the other, to the chassis of the motor vehicle.

[0029] It is common to achieve the attachment of the suspension system to the chassis via a filtering pad made of a material more elastic than steel, typically thermoformed rubbers, elastomer or any other material known to be suitable, in order to reduce the vibrations propagating from the wheel to the chassis.

[0030] Among these different suspension systems, we can for example consider MacPherson strut systems.

[0031] In such a system, the strut firstly comprises a damping cylinder which has a rod mounted to slide in a sleeve. This sleeve is generally fixed to a spindle carrier (wheel side).

[0032] It also includes a spring which is threaded onto the damping cylinder and which is compressed between two stops, including a lower stop which is mounted on the sleeve and an upper stop which is mounted on the rod of the damping cylinder.

[0033] In this example, the upper stop is then intended to be fixed to the vehicle chassis, via the aforementioned filtering block.

[0034] In practice, two main systems for attaching a strut to a chassis are known: one in which the damping cylinder is load-bearing, and the other in which the damping cylinder is non-load-bearing. In both cases, the aforementioned filtering pad is interposed between the strut and the chassis to filter the vibrations generated by the wheel rolling on the granular ground, which travel up the strut to the vehicle chassis.

[0035] In the following, the damping cylinder will be considered to be load-bearing, so that the filter block is sandwiched between the upper stop 30 of the strut and the chassis.

[0036] In [Fig. 2], two upper stops 30, also known as "swivel strut stops," are shown. They could have different shapes from those shown. It should be noted here that each upper stop 30 shown has a cup shape, with a peripheral portion 31 in the shape of a disc and a central hemispherical portion 32.

[0037] On its lower face (spring side), the peripheral part 31 has a projecting circular rib on which the spring can fit.

[0038] On its upper face (chassis side), the peripheral part 31 has stiffening ribs.

[0039] The central part 32 then forms a projecting bulge above the upper face of the peripheral part 31.

[0040] Here, these two central parts 32 and peripheral parts 31 are mounted to rotate flexibly relative to each other (so that the spring can pivot relative to the chassis, particularly when the vehicle turns). Alternatively, the two parts could be fixed relative to each other (and formed as a single piece).

[0041] The filtering pad is here designed to be interposed between the central part 21 of the upper stop 30 and the vehicle chassis. It has a shape of revolution, with a central opening for the passage of the shock absorber cylinder rod.

[0042] This filtering block could take very diverse forms, depending in particular on the shape of the chassis and the upper stop 30, which is why it is not represented here except schematically on [Fig.3].

[0043] The present invention relates more specifically to a device 1 for characterizing the stiffness of such a filter pad 100.

[0044] As shown in [Fig.3], this device 1 is designed to receive two identical filter pads 100 positioned symmetrically.

[0045] It is further intended to be fixed, by means of only these two filter pads 100, in a rigid frame 200 provided for this purpose.

[0046] This device 1 has its own mass. It is thus understood that when the device 1 is excited, it is able to vibrate due to the elastic deformation of the filter pads 100, which makes it possible to carry out the desired measurements.

[0047] We can then describe this device 1 in more detail.

[0048] As shown in Figures 1 and 2, it comprises a body 2 adapted to receive the two upper stops 30 mentioned above in order to block the two filter pads 100.

[0049] As a preliminary matter, we can define an orthonormal frame of reference with respect to this body 2. This frame of reference is centered on the center of gravity of the body 2 and has three orthogonal axes denoted X, Y and Z.

[0050] The body 2 is preferably made from a single piece, for example by molding, casting, machining or even 3D printing.

[0051] It is preferably made of metallic material. Here it is made of steel, which gives it a mass and inertia particularly suited to characterizing the stiffness of the filter pads 100.

[0052] It is preferably axisymmetric in the sense that it exhibits symmetry with respect to the Z-axis. In practice, it has essentially three planes of symmetry that are orthogonal in pairs and intersect at its center of gravity. These are the XY, XZ, and YZ planes.

[0053] The body 2 comprises a central part 10 which has at least one planar region ZI 1, Z12 at which it can be excited in a very precise direction. This central part 10 preferably has two planar regions ZI 1, Z12 at which it can be excited along the Y and X axes. These two planar regions ZI 1, Z12 extend respectively parallel to the XZ and YZ planes.

[0054] The body 2 further comprises two end parts 20 which extend on either side of the central part 10 and which comprise means for centering and holding two filter pads 100 in a symmetrical position with respect to the XY plane.

[0055] The central part 10 could have a spherical shape, with at least two flat surfaces forming the two flat areas. In practice, it would then comprise four flat surfaces arranged in pairs.

[0056] However, preferably (in particular to facilitate stiffness calculations), the central part 10 has a parallelepiped shape, with four lateral faces 11, 12, 13, 14 and two end faces 15, 16.

[0057] It more preferentially presents a cubic shape.

[0058] The two flat areas Z11, Z12, at which the device 1 can be excited, are then provided at the centers of two of the four lateral faces 11, 12. They will thus allow the radial component of the stiffness of each filter pad to be determined.

[0059] Preferably, a relief is provided surrounding at least part of each flat zone Z11, Z12. This relief is provided to facilitate the centering of the tool that will apply the excitation to the body 2.

[0060] In the figures, this relief is formed by a circular rib centered on the face on which it is borne. This rib is continuous here, but alternatively, it could be regularly interrupted. The relief could also alternatively have different shapes. Typically, each flat area could extend in a slight indentation relative to the lateral face on which it is borne, in which case the relief will be formed by the edge of this indentation.

[0061] The end parts 20 of the body 2 extend from the end faces 15, 16 of the central part 10. They preferably have a symmetry of revolution about the Z axis.

[0062] Since the two end parts 20 are identical, only one of them will be described below.

[0063] This end part 20 could be in the form of a simple bar. However, here it has three distinct parts, called sections.

[0064] It mainly comprises a support section 22 on which the upper stop 30 can be mounted. This support section 22 then has the shape of a cylinder of revolution around the Z axis, with a diameter adapted to the upper stop 30.

[0065] Between the central part 10 and this support section 22, the end part 20 includes a stop section 21 on which the central part 32 of the upper stop 30 can rest.

[0066] This stop section 21 has the shape of a cylinder of revolution about the Z-axis, with a diameter greater than that of the support section 22 so as to form the desired bearing. This diameter is designed to be as close as possible to the width of the central part 10 (to give the body 2 a shape as close as possible to a sphere). It is slightly less than this width, so that a gap remains between this stop section 21 and the rib carried by the peripheral part 31 of the upper stop 30.

[0067] Finally, the end part 20 has, on the side opposite the stop section 21, a free end section 23, which is a cylinder of revolution about the Z axis, and of a diameter smaller than that of the support section 22. This free end section 23 is threaded so as to be able to accommodate a nut 33. Here, it is an M12 type thread.

[0068] This nut 33 thus allows the upper stop 30 to be locked in contact with the stop section 21.

[0069] In summary, the means for centering and holding each filter pad 100 then include the upper stop 30, as well as the nut 33.

[0070] We can give here, as an example, the dimensions of the steel body 2.

[0071] In this example, the central cubic part 10 has a width of 60 mm, the stop section 21 has a length of 20 mm and a diameter of 50 mm, the support section 22 has a length of 26 mm and a diameter of 20 mm, and the free end section 23 has a length of 28 mm and a diameter of 12 mm.

[0072] As shown in [Fig.4], thanks to these dimensions, the rigid body modes of body 2 are included in a frequency band from 50 to 350 Hz, and more precisely here from 60 to 300 Hz regardless of the direction of measurement, which corresponds to the frequencies of rolling noises of a motor vehicle.

[0073] We have indeed represented on this [Fig.4] a curve Clx illustrating the amplitude of the vibrations of the body 2 along the X axis when the latter is excited, and, similarly, curves Cly and Clz illustrating the vibration amplitudes of the body along the Y and Z axes.

[0074] However, it can be seen in [Fig. 4] that the first elastic deformation mode of body 2 (the one with the lowest frequency) has a frequency much higher than that of the last rigid body mode of body 2 (the one with the highest frequency). The frequency of this first elastic deformation mode of body 2 is indeed on the order of 5500 Hz, or more than 10 times the frequency of the last rigid body mode of body 2. In practice, body 2 will be designed so that the difference between these two frequencies is at least greater than 1000 Hz, in order not to distort the analysis of the measured data.

[0075] As shown in [Fig. 3], the test bench used comprises a frame 200 (typically a marble slab). It also comprises two chucks 201 adapted to lock the device 1 via the two filter pads 100. For example, one of these chucks can be fixed to the frame 200 while the other is movable in translation along the Z-axis, by means of a linear actuator.

[0076] These two mandrels 201 are designed to bear against the two filter pads 100 in the same way that the chassis of a vehicle rests on these filter pads. They for this purpose they may include for example two clamping jaws allowing the clamping of interface parts of corresponding shapes.

[0077] In the embodiment considered here, the chucks are provided to apply, via the aforementioned linear actuator, an axial preload (along the Z axis) on the two filter pads 100 corresponding to the weight that the chassis of a vehicle exerts on such a filter pad 100 (on the order of several thousand Newtons).

[0078] The test bench also includes a force sensor adapted to measure the preload exerted by the chucks so as to be able to adjust this preload to the desired value.

[0079] The test bench also includes an excitation tool and a vibration sensor.

[0080] The excitation tool can for example be formed by an impact hammer or a vibrating pot, adapted to come into contact with each of the flat areas ZI 1, Z12.

[0081] The vibration sensor can be formed by a tri-axis accelerometer, with a sensitivity for example equal to 100 mV / g.

[0082] Finally, the test bench is equipped with a computer system programmed to characterize the stiffness of each filter pad 100 by modal analysis, in accordance with the following method.

[0083] This method first involves a step of placing the two filter pads 100 in a symmetrical position on the device 1, against the two upper stops 30.

[0084] It continues with a step of locking the assembly on the test bench, between the mandrels 201. At the end of this step, the mandrels are in contact only with the two filter pads 100. They are not in contact with the body 2, nor with the upper stops 30. They also exert a preload along the Z axis.

[0085] The excitation tool is then placed against one of the flat areas ZI 1, Z12, so that it can successively emit several trains of vibrations, at different frequencies, on the body 2. During this step, the vibration sensor records the vibrations of the body 2.

[0086] This step is repeated on the other of the planar zones ZI 1, Z12. It can also be repeated outside these planar zones (to determine a conical component of the stiffness of the filter pads).

[0087] Finally, the computer system processes the measured data and makes it possible to determine the radial component of the stiffness of each filter pad 100, based in particular on the measurement of the frequencies of the rigid body modes of the system.

[0088] The present invention is in no way limited to the embodiment described and represented, but a person skilled in the art will be able to make any variation in accordance with the invention.

[0089] Typically, the mandrels could also be adapted to excite the body along the Z axis, so as to allow the axial component of the stiffness of each filter pad to be determined.

[0090] Furthermore, it should be noted that if the invention makes it possible to characterize the stiffness of a filtering block of a strut suspension system, it will also be usable to characterize the stiffness of a filtering block of another type of suspension system (double triangulation suspension, multi-link suspension...).

Claims

Demands

1. Device (1) for characterizing the stiffness of a suspension mount (100) of a motor vehicle, comprising: - a central part (10) which has substantially three orthogonal planes of symmetry (XY, XZ, YZ) and which includes at least one flat area (Z11, Z12) parallel to one of said planes of symmetry (XZ, YZ), and - two end parts (20) which extend on either side of the central part (10), which have means for centering and maintaining two mounts (100) in a symmetrical position with respect to another of said planes of symmetry (XY) and which each have a variable diameter, maximum at its junction with the central part (10).

2. Device (1) according to claim 1, wherein the central part (10) has a parallelepiped shape, with six faces (11, 12, 13, 14, 15, 16) one of which carries said flat area (Z11, Z12).

3. Device (1) according to claim 2, wherein the central part (10) has a cubic shape.

4. Device (1) according to any one of claims 2 and 3, wherein each planar zone (Z11, Z12) extends to the center of one of the faces (11, 12) of the central part (10).

5. Device (1) according to any one of claims 1 to 4, wherein each end part (20) has rotational symmetry about an axis (Z).

6. Device (1) according to any one of claims 1 to 5, wherein each end part (20) has, at a free end, a threaded part (23), and wherein said centering and retaining means comprise a suspension stop (30) engaged on each end part (20), and a nut (33) screwed onto each threaded part (23) so as to lock said suspension stop (30).

7. Device (1) according to any one of claims 1 to 6, wherein each flat area (Z11, Z12) is at least partially surrounded by a protruding relief.

8. Device (1) according to any one of claims 1 to 7, wherein there are provided at least two planar zones (Z11, Z12) respectively parallel to two of said planes of symmetry.

9. Device (1) according to any one of claims 1 to 8, wherein the central part (10) and the two end parts (20) form a single-piece body (2) shaped such that the rigid body modes and the elastic deformation modes of said body (2) are respectively located in distinct frequency bands.

10. A method for characterizing the stiffness of a block (100) by modal analysis, wherein the following steps are provided: - locking two pads (100) in a symmetrical position on a device (1) for characterizing the stiffness of a pad (100) of a motor vehicle suspension, comprising, on the one hand, a central part (10) which has substantially three orthogonal planes of symmetry (XY, XZ, YZ) and which includes at least one flat area (Z11, Z12) parallel to one of said planes of symmetry (XZ, YZ), and, on the other hand, two end parts (20) which extend on either side of the central part (10) and which include means for centering and maintaining the two pads (100) in a symmetrical position with respect to another of said planes of symmetry (XY), - blocking the two pads (100) in a fixed frame (200), - applying an excitation to the flat area (Z11, Z12), - vibration measurement of the device (1), and - determination of the stiffness of each pad (100) based on the vibration measurements taken.

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