Device and method for characterizing the stiffness of a motor vehicle suspension stud

Abstract

The invention relates to a device for characterizing the stiffness of a motor vehicle suspension mount, comprising: - a central part (10) which has substantially three orthogonal planes of symmetry (XY, XZ, YZ) and which comprises at least two flat zones (Z11, Z12) respectively parallel to two first of said planes of symmetry, and - two end parts (20) which extend on either side of the central part (10) and which comprise means for centering and maintaining two mounts in a symmetrical position relative 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 motor vehicle suspension stud 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 motor vehicle suspension stud. State of the art

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

[0004] Different suspension systems are known.

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

[0006] Such a strut generally comprises a cylinder for damping the stresses, and a spring threaded around the cylinder.

[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 stud generally made of elastomer.

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

[0009] This plot is found in other suspension systems.

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

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

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

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

[0014] It is understood that in order to carry out these measurements, it is necessary to exert a preload on the plot, corresponding to a quarter of the weight of the car if it has four wheels, then to apply vibration excitation along an axis separate from the preload, while carrying out measurements, which proves complicated when seeking to obtain precise 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 motor vehicle suspension stud, comprising: - a central part which has substantially three orthogonal planes of symmetry and which comprises at least one flat zone parallel to one of said planes of symmetry, and - two end parts which extend on either side of the central part and which comprise means for centering and maintaining two pads in a symmetrical position relative to another of said planes of symmetry.

[0016] Thus, the invention proposes a measuring device by modal analysis which comprises a central part of adapted mass and which accommodates not a single plot, but two plots in symmetrical positions.

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

[0018] Other advantageous and non-limiting characteristics of the device according to the invention, taken individually or in all technically possible combinations, are the following: - 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 symmetry of revolution 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 block said suspension stop; - each flat area is at least partially surrounded by a projecting relief; - at least two flat areas are provided, respectively parallel to two of 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 frequency bands distinct.

[0019] The invention also proposes a method for characterizing the stiffness of a plot by modal analysis, in which steps are provided: - locking two pads in a symmetrical position on a device such as the aforementioned, - blocking of the two plots in a stationary frame, - application of an excitation to one then the other of the two flat zones, - vibration measurement of the device, and - determination of the stiffness of each pad based on the vibration measurements carried out.

[0020] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Detailed description of the invention

[0021] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

[0022] In the attached drawings:

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

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

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

[0026] [Fig.4] is a graph illustrating the variations of the vibration amplitudes of the body of [Fig.l], 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 secured, on one side, to the wheel and, on the other, to the chassis of the motor vehicle.

[0029] It is common to secure the suspension system to the chassis via a filtering pad made of a material more elastic than steel, typically thermoformed rubber, 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 type strut systems.

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

[0032] It also comprises 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 chassis of the vehicle, via the aforementioned filtering stud.

[0034] In practice, two main systems are known for attaching a strut to a chassis, a first in which the damping cylinder is load-bearing, and a second 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 which are generated by the rolling of the wheel on the granular ground and which rise along the strut towards the chassis of the vehicle.

[0035] In the following, it will be considered that the damping cylinder is a carrier, so that the filtering pad is sandwiched between the upper stop 30 of the strut and the chassis.

[0036] In [Fig. 2], two upper stops 30 are shown, also known as “rotating strut stops”. They could have different shapes from those shown. It will be noted here that each upper stop 30 shown has a cup shape, with a disc-shaped peripheral part 31 and a hemispherical central part 32.

[0037] On its lower face (spring side), the peripheral part 31 has a projecting circular rib onto 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 protruding bulge above the upper face of the peripheral part 31.

[0040] Here, these two central 32 and peripheral 31 parts are mounted to be able to rotate relative to each other (so that the spring can pivot relative to the chassis, in particular when the vehicle turns). Of course, as a variant, the two parts could be fixed relative to each other (and come from a single piece).

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

[0042] This filtering pad could come in very diverse forms, depending in particular on the shape of the chassis and the upper stop 30, which is the reason why which is not represented here other than schematically in [Fig.3].

[0043] The present invention relates more specifically to a device 1 making it possible to characterize the stiffness of such a filtering 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 provided to be fixed, by means of only these two filtering 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 taking into account 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 aforementioned upper stops 30 in order to block the two filtering pads 100.

[0049] As a preliminary point, we can define an orthonormal reference frame with respect to this body 2. This reference frame is centered on the center of gravity of the body 2 and comprises three orthogonal axes noted 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 has symmetry with respect to the Z axis. In practice, it has substantially three orthogonal planes of symmetry in pairs, which intersect at its center of gravity. These are the XY, XZ and YZ planes.

[0053] The body 2 comprising a central part 10 which has at least one flat zone ZI 1, Z12 at which it can be excited in a very precise direction. This central part 10 preferably has here two flat zones ZI 1, Z12 at which it can be excited along the Y and X axes. These two flat zones 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 maintaining two filtering pads 100 in a symmetrical position relative to the XY plane.

[0055] The central part 10 could have a ball shape, with at least two flats forming the two flat areas. In practice, it would then comprise four flats opposite each other 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 preferably has a cubic shape.

[0058] The two flat zones Z1 1, 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 make it possible to determine the radial component of the stiffness of each filtering pad.

[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 which will apply the excitation to the body 2.

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

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

[0062] The two end parts 20 being identical, only one of them will be described below.

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

[0064] It mainly has 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 comprises 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 around the Z axis, with a diameter greater than that of the support section 22 so as to form the desired support. This diameter is here intended 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 ball). It is here 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 around the axis Z, and of 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 a thread of type M12.

[0068] This nut 33 thus makes it possible to block the upper stop 30 in support against the stop section 21.

[0069] In summary, the means for centering and maintaining each filtering pad 100 then comprise the upper stop 30, as well as the nut 33.

[0070] Here we can give 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, support section 22 has a length of 26 mm and a diameter of 20 mm, and 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 the body 2 are included in a frequency band ranging from 50 to 350 Hz, and more precisely here from 60 to 300 Hz regardless of the direction of the measurement, which corresponds to the frequencies of the rolling noise of a motor vehicle.

[0073] In fact, this [Fig.4] shows 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] On the other hand, we note in this [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 in fact of 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 greater than at least 1000 Hz, so as not to distort the use 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 mandrels 201 adapted to block the device 1 by means of the two filtering pads 100. For example, one of these mandrels can be fixed to the frame 200 while the other is movable in translation on the latter 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 bears on these filter pads. For this purpose, they may comprise, for example, two clamping jaws allowing the clamping of interface parts of corresponding shapes.

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

[0078] The test bench also includes a force sensor adapted to measure the preload exerted by the mandrels 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 zones Z1 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 firstly comprises 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 blocking 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 zones Z11, Z12, so that it can successively emit several vibration trains, 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 flat zones Z11, Z12. It can also be repeated outside these flat 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 filtering pad 100, in particular from 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 shown, but those skilled in the art will be able to provide any variant 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 will be noted that if the invention makes it possible to characterize the stiffness of a filtering pad of a strut suspension system, it will also be usable for characterize the stiffness of a filtering block of another type of suspension system (double wishbone suspension, multi-link suspension, etc.).

Claims

Claims

1. Device (1) for characterizing a stiffness of a motor vehicle suspension stud (100), comprising: - a central part (10) which has substantially three orthogonal planes of symmetry (XY, XZ, YZ) and which comprises at least one flat zone (ZI 1, 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) and which comprise means for centering and maintaining two studs (100) in a symmetrical position relative to another of said planes of symmetry (XY).

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

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

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

5. Device (1) according to one of claims 1 to 4, in which each end portion (20) has a symmetry of revolution around an axis (Z).

6. Device (1) according to one of claims 1 to 5, in which each end portion (20) has a variable diameter, which is maximum at its junction with the central portion (10).

7. Device (1) according to one of claims 1 to 6, in which each end part (20) has, at a free end, a threaded part (23), and in which said centering and holding 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 block said suspension stop (30).

8. Device (1) according to one of claims 1 to 7, in which each flat zone (Z11, Z12) is at least partially surrounded by a projecting relief.

9. Device (1) according to one of claims 1 to 8, in which at least two flat zones (Z11, Z12) are provided, respectively parallel to two of said planes of symmetry.

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

11. Method for characterizing the stiffness of a pad (100) by modal analysis, in which steps are provided for: - blocking two pads (100) in a symmetrical position on a device (1) according to one of claims 1 to 10, - blocking the two pads (100) in a stationary frame (200), - applying an excitation to the flat zone (ZI 1, Z12), - vibration measurement of the device (1), and - determining the stiffness of each pad (100) as a function of the vibration measurements carried out.

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