FR2693273A1 - Measuring acceleration of vehicle - Google Patents

Abstract

The method involves measuring the instantaneous fluid pressure (Pa) in hydraulic or hydropneumatic components (16) for transferring forces between the chassis components and body work. A vehicle acceleration value is derived from the fluid pressure measurements.The components of the acceleration parallel to the directions of force transfer are determined by subtracting a constant average pressure value from the measured value to give a dynamic pressure value which is then multiplied by a factor dependent on the vehicle construction to form the parallel component.

Description

METHOD AND DEVICE FOR DETERMINATION
ACCELERATION OF A VEHICLE SUPERSTRUCTURE
The present invention relates to a method and a device for determining the acceleration of a vehicle superstructure.

 On vehicles, more and more control systems are installed, which have an influence on essential service parameters of the vehicle, such as braking behavior (anti-lock braking system), driving behavior (automatic systems traction control), as well as on the development of the chassis (adaptive, semi-active or active chassis control systems). In the case of control systems of this type, information on the instantaneous state of the movement of the vehicle is required, as input quantities, particularly information on the instantaneous position, the instantaneous speed, as well as the instantaneous acceleration of vehicle components.

Of this information, that concerning the acceleration of the bodywork is of particular importance. By their very nature, regulation systems are often relatively inert, particularly due to the large mass of the bodywork, so that the acceleration of the vehicle superstructure, indicating the tendency of the state of motion to change of the bodywork, constitutes an input value, which allows the regulation system considered to give a rapid response, on the modifications of state of the system.

The mentioned input quantities (trajectory, speed, acceleration) can be obtained using various sensors. Document DE-A-37 40 792 shows for example an ultrasonic sensor, which gives the spacing of the bodywork on the ground. Document DE-C-38 18 188 also uses a displacement sensor 2, which indicates the instantaneous spacing between the bodywork and the vehicle wheel, as well as a sensor 1 for the acceleration of the wheel and a sensor 3 for acceleration of the superstructure or bodywork. These measured quantities are routed to an active suspension system as input quantities. Patent EP-BO 249 209 deals with an active chassis control system which uses sensors for the acceleration of the vehicle superstructure. A regulation signal is derived from this sensor signal, by the fact that a weighted sum is formed from this signal as well as an integration value with respect to the time of this signal (Figure 5). One thus obtains, without using an own speed sensor, a compound regulation signal, which depends as much on the acceleration of the superstructure, measured, as on the superstructure speed, calculated. The document
EP-A-0 431 597 describes an active chassis control, which uses acceleration sensors 15, for the vertical acceleration of the superstructure. In addition, displacement sensors 14 are provided, which measure the relative spacing between the chassis wheels and the bodywork. Finally, pressure sensors 13 are also provided, which measure the instantaneous pressure inside pneumatic shock absorbers. , by means of which the body rests on the wheel in question The pneumatic shock absorbers are filled with liquid, which due to a gas bag pressure accumulator, is constantly under pressure.

The signals from the four pressure sensors are combined with each other, forming sums and difference values, in order to obtain information on the rotational movements of the vehicle body.

 Conventional acceleration sensors work most of the time according to the principle of inertia, that is to say that the forces exerted on the sensor housing are measured by a test mass mounted mobile in the sensor, for example using strain gauges. The construction costs, from the mechanical as well as the electrical point of view, for acceleration sensors of this type, are relatively high, which comes fully into consideration for the mass production product that is a motor vehicle. , each with four acceleration sensors.

 This is why the present invention aims to provide a method for determining an acceleration of a vehicle superstructure, which is satisfied with reduced additional construction costs.

 This problem is solved, on a vehicle comprising hydraulic or hydropneumatic components for transmitting forces between the chassis and the vehicle body, by the fact that the pressure of the fluid prevailing momentarily in the component under consideration is measured and that deduces, from the measured fluid pressure, a vehicle acceleration value.

 This is based on the idea that the pressure of the fluid measured directly reflects the force exerted between the wheel of the chassis in question and the point of attachment of the component to the body of the vehicle. This force tries to move the two masses, the body and the chassis, away from each other. In the case of two freely movable masses, one then obtains for the resulting acceleration, for example of the mass of the bodywork, a value depending on the mass ratio. The mass of the chassis is not, however, freely mobile, but rather rests on the ground, in a more or less strongly damped manner, so that the influence of the mass of the chassis decreases accordingly (in the extreme case of the rigid support of the chassis on the ground, the acceleration of the body depends only on the mass of the body). In the concrete case, it is possible to determine, by calculation or on the basis of tests, the dependence of the acceleration of the superstructure of the force exerted and thus of the fluid pressure measured. This dependence can be given, in most cases, to a satisfactory accuracy, by a constant multiplication factor.

Fluid pressure can be measured with inexpensive, reliable, commercially available fluid pressure sensors. In the case of active chassis regulation systems, which a priori use pressure sensors, these pressure sensors can also be used as they are, for the determination, according to the present invention, of a vehicle acceleration value, so no additional construction costs are created. From the determined acceleration values of the vehicle, it is possible, by forming sums and corresponding differences, to also determine acceleration values for a rotational movement of the bodywork around the longitudinal axis or the transverse axis.

 As an improvement of the present invention, it is proposed to determine the parallel component of the acceleration of the superstructure of the vehicle, parallel to the direction of transmission of the forces of the component considered, by subtracting, from the value of pressure of the measured fluid, a value constant average pressure, to form a dynamic pressure value, and multiplying the dynamic pressure value by a predetermined factor, depending on the chassis design, to form the parallel component. In general, the hydraulic or hydropneumatic components (in particular pneumatic shock absorbers) are oriented essentially in the vertical direction, so that, therefore, the determined acceleration value directly indicates the vertical acceleration component of the acceleration of the vehicle superstructure. This value is of decisive importance, especially for chassis control systems. In the case of components, particularly pneumatic shock absorbers, which also support at least part of the body weight, the constant average pressure value must be subtracted from the measured fluid pressure value. As already mentioned above, the multiplication factor depends on the overall design of the chassis, i.e. the masses involved, as well as the nature of the interactive support and the support in relation to the ground. The acceleration component determined then indicates according to which acceleration the body moves down or up, from its constant average level.

 The method according to the present invention is used both on single-acting piston rod-cylinder units and on double-acting cylinder rod-piston units, on which the piston separates two closed cylinder interior spaces. The pushing force is then proportional to the difference of the piston surfaces on the two sides of the piston, insofar as the pressure is the same in the two interior cylinder spaces. On vehicles, shock absorber legs are often used, i.e. cylinder-piston rod units, filled with liquid, under gas pressure, with a piston at the inner end of the piston rod. , which separates two interior cylinder spaces from each other. A connecting channel, having a throttling point which can be regulated if necessary, connects the two interior cylinder spaces, so that a damping force depending on the displacement speed of the piston. In this case, momentarily different pressures in the two interior cylinder spaces can be created. In order to be able to determine, in accordance with the present invention, the vertical component of the acceleration of the vehicle superstructure, in the case of a hydropneumatic component of this type, it is proposed to measure the fluid pressure prevailing momentarily in each interior space of cylinder and use, as instantaneous fluid pressure of the component, the difference in fluid pressures, weighted correspondingly to the active piston surfaces.This instantaneous fluid pressure exactly indicates the momentary thrust force of the component, so that the desired acceleration value is again obtained directly, after multiplication by the predetermined multiplication factor.

 The present invention also relates to a device for implementing the method described above, with at least one fluid pressure sensor, for measuring the fluid pressure, in a hydraulic or hydropneumatic component for transmitting forces between chassis and bodywork, a subtraction member, for determining a dynamic pressure value by subtracting an average pressure value from the measured fluid pressure value, and a multiplication member, for determining a parallel component of the acceleration of the vehicle superstructure, parallel to the direction of the force transmission of the body considered, by multiplying the dynamic pressure value by a predetermined factor.

 On a vehicle comprising a displacement sensor to determine the distance considered, between a part of the chassis and the bodywork, the above-mentioned problem is solved by the fact that an instantaneous speed value is deduced from the measured instantaneous spacing value , by differentiation as a function of time, and that an acceleration value of the superstructure is determined, by forming a weighted sum of the instantaneous spacing value and the instantaneous speed value, according to predetermined weighting factors. This is based on the idea that the displacement parameter, which constitutes the spacing between the chassis part and the bodywork, can be measured in a particularly simple manner, by means of appropriate commercially available displacement sensors, and that the acceleration of the superstructure depends, in a certain way, on the distance measured. A double differentiation as a function of time, of the measured position deviation, certainly does not lead directly to the vertical acceleration of the superstructure, desired (by referring to a terrestrial, static reference system), but only to the relative acceleration between the chassis and the superstructure. The superstructure acceleration can, however, be obtained as a weighted sum of the relative spacing, as well as the relative speed, which can be determined in a simple manner and according to the required precision, by differentiation as a function of time. of the distance measured. The weighting factor of the sum for the relative speed depends on the elasticity rate of the suspension acting between the bodywork and the chassis, and the weighting factor of the sum for the relative trajectory, of the corresponding damping constant.

 The present invention finally also relates to a device for implementing the above-mentioned method, with a displacement sensor, for determining the spacing between a part of the chassis and the bodywork, a member of differentiation as a function of time, for the value d measured instantaneous spacing, to form an instantaneous speed value and a summing member, to form a weighted sum of the instantaneous spacing value and the instantaneous speed value. This device is inexpensive, for a simple structure, since the displacement sensor, compared for example to an acceleration sensor, is of a much simpler structure and therefore cheaper. The differentiation device, as well as the summation device, can be integrated into the electronic control, particularly in the active regulation of the chassis.

 The present invention is described below with the aid of exemplary embodiments.

Figure 1 is a very simplified side schematic view of a motor vehicle with a device for determining the acceleration of the superstructure by measuring fluid pressure
Figure 2 shows a two mass system
FIG. 3 schematically shows the determination of the acceleration of the superstructure, according to FIG. 1, using a hydraulic gas shock absorber
FIG. 4 shows the variation curve as a function of time of a fluid pressure value;
FIG. 5 is a diagram of another device for determining an acceleration of the vehicle superstructure using a measured spacing value;
FIG. 6 shows a variation curve as a function of time, of the acceleration of the superstructure, determined using the device according to FIG. 5, with respect to the acceleration of the actual superstructure.

On vehicles, in particular on road vehicles, such as passenger vehicles, more and more regulation systems are used, which serve to increase driving safety, but also, in many cases, to increase comfort. driving. Anti-lock brakes and traction control systems are already widely used. In addition to this, more and more regulation systems are also used, which are involved in the development of the chassis. A distinction is made here between adaptive, semi-active and active systems. In this context, we will refer to the reference article by Karnopp Crosby,
Herwood "Vibration control using semi-active force generators" ASME-Journal of Engineering for Industry,
Transactions of the ASME-n "96, 1974, pages 619 to 626.

 For the quality of the regulation considered, the fact of knowing as precisely as possible the instantaneous state of the movement of the vehicle is of great importance, particularly the fact of knowing the instantaneous relative spacing of the superstructure and the chassis, and the instantaneous relative speed between the two elements, as well as knowing the instantaneous acceleration of the superstructure, resulting for example from cornering, as well as braking and acceleration maneuvers, which act on the vehicle.

In the mass-produced product of a motor vehicle, the simplest possible structure of the control systems, including sensors, is very important. Likewise, from the point of view of reliability, a structure comprising as few components as possible, particularly sensors, is desired, since the risk of a fault inside the system increases with the number of components.

 FIG. 1 shows, according to a non-detailed diagram, a side view of a motor vehicle 10, the superstructure or body of which bears the reference 11 and the chassis of which is represented, purely schematically, by a front wheel support 12a, thus only by a rear wheel support 12b, which, by means of a usual suspension and vibration damping system - symbolized by a spring 14, as well as by a damping member in the form of a unit piston rod cylinder 16 - rests on the body 11.

The piston rod-cylinder unit 16 may, as shown, for simplicity, correspond to the single-acting piston type, or as suggested in FIG. 3, correspond to the double-acting piston type. The fluid, generally liquid, located in the interior space 18 limited by the piston, as well as by the cylinder, can undergo a gas pressure, as is also suggested in FIG. 3, so that the unit In this case, the piston rod cylinder supports part of the weight of the vehicle. In the case where the device, described below in even more detail, is used to determine the acceleration of the vehicle superstructure, in connection with a chassis regulation system, the cylinder rod-piston unit 16 can each time be coupled with a chassis regulation device, generally referenced by C. Here, we take into account, in the case of 'A simpler embodiment, the regulation of the damping of the cylinder-piston rod unit, such as this will be further explained below, with the aid of Figure 3.

The interior space can however be connected to an external pressure source (symbolized by a pump 17, inside the regulating device C), which imposes the internal pressure inside the cylinder-piston rod unit 16 and thus actively influences the forces acting between the chassis and the body. In an extreme case, the cylinder-piston rod unit acts purely as a position or displacement sensor, which defines the instantaneous spacing between the bodywork 11 and the wheel support considered 12a or 12b. In regulation systems of another type, the cylinder-piston rod unit 16 may however be an independent component of the regulation device considered, particularly a hydraulic gas shock absorber (in this case, the fluid connection lines 20 shown in Figure 1 would disappear).

According to the present invention, a pressure sensor 24 is connected, as part of a device 26 for determining the vertical acceleration of the vehicle superstructure, indirectly or via a fluid connection line 22 suggested in FIG. 1, to the interior space 18 of the cylinder rod-piston unit 16. The sensor signal emitted by the pressure sensor 24, indicating the instantaneous fluid pressure in the cylinder rod-piston unit 16, is routed, via an electrical connection line 28, to a subtraction member 30, which subtracts from the sensor signal, indicating the value of fluid pressure measured Pa, a value of constant average pressure Pg. This difference gives a value dynamic pressure P. The corresponding output signal from the subtraction member 30 is then routed, via a line 32, to a multiplication member 34, which multiplies the signal corresponding to the dynamic pressure
P by a predetermined factor C. This product corresponds to the vertical acceleration z2 of the superstructure, desired. The signal obtained is sent from the device 26, via a line 36, to the regulation device C used, considered. In Figure 1, the device 26 just described, is shown in detail only on the front wheel support 12a.

A corresponding device 26 for determining the vertical acceleration in the region of the rear wheel support 12b is only partially shown, for the sake of simplicity. Consequently, in the case of a suspension with independent wheels, four devices of this type 26 will have to be mounted as a whole, in the regions of the four wheels. From the vertical acceleration measured, it is possible, by correspondingly subtracting and summing, to determine the acceleration of the rotational movement of the vehicle around the longitudinal axis, as well as around the axis transverse.

 The ideas underlying the device 26 previously described are explained below with the aid of FIG. 2.

The internal pressure P prevailing in the cylinder-piston rod unit 16 considered, multiplied by the active surface of the piston (cross-section of the piston q) directly gives the force F which is exerted, via the cylinder unit -piston rod 16, of the wheel support 12 on the body 11 and vice versa. This force would however be identical to the force accelerating the bodywork, only if the cylinder-piston rod unit 16 was directly supported on the ground U. A somewhat realistic model is given in FIG. 2. Here, the share of the body mass is designated by m2 and the mass of the corresponding part of the chassis (wheel support 12 plus wheel 13 and other structural elements mounted on the wheel support 12) per ml. The force F, acting between the two masses, is symbolized by a helical spring. Due to this force, the mass m2 is moved away from the mass ml according to an acceleration indicated by the arrow x2.

Correspondingly, the mass ml is moved in the opposite direction according to the acceleration xl. It is possible to deduce for the acceleration x2 the following relation

In application to the assembly according to FIG. 2, for the vertical acceleration z2 of the bodywork 11, the fact is obtained that the latter, proportional to the force (= pq) and thus proportional to the measured pressure P, is equal to
z2 = P .C,
the proportionality factor C taking the following value

 Since, unlike FIG. 2, the mass of the chassis ml is not freely movable, but rests on the ground U, by means of the wheel 13 undergoing a movement (symbolized by a compression spring 15), the constant C must still be modified accordingly, on the basis of corresponding calculations or driving tests.

 As mentioned above, the piston rod-cylinder unit 16 can also consist of a conventional gas hydraulic shock absorber, such as that, marked with the reference 50, shown in a roughly simplified manner in FIG. 3. A piston 56 mounted at a piston rod end of a piston rod 52, inside a closed cylinder 54, divides the interior space of the cylinder into an interior space of the upper cylinder 58, as well as a lower interior cylinder space 60. The piston rod 52 comes out at the end of the upper cylinder 54, in FIG. 3, in a sealed manner towards the outside thereof. Pressurized fluid, in particular pressurized liquid 62, inside the cylinder 54, is under pressure due to a pressure pocket containing compressed gas 64.

This pressure pocket 64 is provided in the schematic drawing shown, at the upper end of the cylinder 54 and separated from the interior of the upper cylinder 58 by an annular separation piston 66. The separation piston 66 is mounted so that it can move the interior of the cylinder 54 in the direction of the axis of the cylinder and sealed as well with respect to the peripheral interior surface as with respect to the peripheral exterior surface of the piston rod 52. The pressure pocket can also be arranged at a another location, particularly be provided at another location in the annular space of a cylinder shaped with two walls or separated from the cylinder-piston rod unit 50 with fluid connection to the two interior spaces 58, 60 (see also for example document EP-A-0 431 597).

 The two interior cylinder spaces 58, 60 are connected to each other, either by means of a corresponding passage 68 of the piston 56, or by an exterior line 70, represented in FIG. 3 by dots. The piston rod 52 is then pushed by a force F, which is equal to the product of the internal pressure P by the difference of the frontal surfaces Al or A2 of the piston 56 delimiting the interior spaces of cylinder 60 and 58. To dampen the movement of outlet and inlet of the piston, a throttling point D is however provided in passage 68 or in the outer line, which slows the flow, depending on the flow speed. chassis, an adjustable butterfly valve 72 which is connected by a line 74 shown in phantom with the regulating device C, can also be mounted inside the connecting line 70.

Due to the constant or regulated throttling point D, it is created, at least in the cases of high exit or entry speeds of the piston rod 52, momentarily a different pressure in the two interior spaces of cylinder 58 and 60. In order to be able to measure, in a sufficiently precise manner also in this case, the instantaneous thrust force F, the fluid pressures in the two interior cylinder spaces 58 and 6Q are each recorded for themselves. This is suggested in FIG. 3 by two pressure sensors 76 and 78, which respectively measure the pressure P1 in the interior of the lower cylinder 60 or the pressure
P2 in the interior of the upper cylinder 58. The two measurement signals are routed, by lines 80, 82, to a differentiating member 84, which determines the momentary fluid pressure Pa representing the thrust force F according to the relationship next

 the lower front surface of the piston 56 being designated by A1 and the upper front surface of the piston, of annular shape, being designated by A2.

The differentiation member 84 is connected, by a line 85 corresponding to the line 28 of FIG. 1, to the subtraction member 30, as part of the device 26 if not unchanged and therefore not shown in detail in the figure 3.

 In FIG. 4 is shown a variation as a function of time, possible, of the pressure Pa measured directly, according to FIG. 1, or derived from the pressures P1 and P2 according to FIG. 3, in the form of a curve 86.

During the stopping of the vehicle, until time t0, a constant pressure value Pg is obtained, which is proportional to the share of the weight of the vehicle m2 and to the terrestrial acceleration, from which, if necessary, the spring force exerted by the spring 14. From the instant t0, the vehicle is in motion (direction of arrow A in FIG. 1), with the consequence that pressure oscillations are created corresponding to the faults of flatness of the ground, but also caused by centrifugal and pitching forces, when cornering or when braking or accelerating. Since constant gravity is of no interest for regulation, the constant pressure value Po is subtracted from the measured pressure value Pa, which amounts to moving, from the value Pg, the abscissa axis of FIG. 1 upwards. Depending on whether the actual pressure value P = Pa - Po is greater or less than Po, forces are exerted by the chassis on the bodywork, oriented vertically upwards, or vertically downwards, resulting in an acceleration z2 , which is each time proportional to the magnitude of the difference P. The portion of weight supported in this case by the spring 14 and if necessary by the hydraulic gas spring can be considered to be constant, since these structural parts work, in due to a high spring preload, in a part of the spring characteristic extending to a large extent horizontally.

 The device explained above with the aid of FIGS. 1 to 4, for determining the vertical acceleration of the superstructure, requires only low construction costs, namely a pressure sensor including the corresponding operating circuits. In the case of regulation systems, particularly in the case of chassis regulation systems, in which pressure sensors of this type are already used for monitoring the regulation of the chassis, these can be used as is, for measuring the acceleration of the superstructure, which does not require any other sensor to be fitted.

 According to the second embodiment of the present invention, described below, a conventional inertia sensor is also not used to determine the acceleration of the superstructure. In this case, the output signal is emitted by a position or displacement sensor 110, which measures the instantaneous spacing zrel, between the part of the chassis considered and the bodywork.

Displacement sensors of this type are simple and inexpensive in structure and reliable in operation. This is why the possibility arises, of mounting the displacement sensor 110 in the region of the superstructure shock absorber (shock absorber leg or hydraulic gas shock absorber), as shown in very simplified form on the FIG. 5 and designated by the reference 112. The displacement sensor 110 is for example fixed on the bodywork and comes into engagement with the element of the shock absorber connected to the part of the chassis (the tube forming cylinder in FIG. 5), which is symbolized by a corresponding feeler roller 114.

Several common measurement principles can be used, such as the use of an electric friction contact.

 The device generally designated by 116 for measuring the acceleration of the vertical superstructure z2, further comprises a differentiation member 118, which deduces, from the output signal of the path sensor 110 giving the spacing zrel, via time differentiation, a signal indicating the speed zrel of the relative movement between the superstructure and the chassis part. This signal, as well as additionally the signal from the displacement sensor 110, is routed to a summing member 120, to form a weighted sum from the instantaneous spacing value zrel and the momentary speed value zrel. via an output line 122 shown in dashed lines, the output signal from the summing member 120 is routed as an output signal from the device 116 to a regulation device not shown, particularly to the regulation of the chassis .

 The idea behind this type of determination of the acceleration of the superstructure lies in the fact that it is certainly not possible to deduce the acceleration of the vertical superstructure z2 directly from the measurement of zrel by double differentiation as a function of time, since zrel as the difference of the z2 coordinates of the superstructure and the zl coordinates of the chassis part with the mass ml, is different from z2. However, it can be shown that the following relation applies to the acceleration of the superstructure.

z2:
z2 = (- k2. zrel - c2. zrel) / m2),
k2 denoting the damping constant of the superstructure damper 112 and c2 the spring constant of a superstructure spring 124, acting between the masses m2 and ml, and zrel indicating the first derivative of zrel as a function of time.

This relationship is independent of the momentary spacing h of the mass ml, of the ground U, and also independent of the spring effect of the tire, not shown, symbolized by a tire spring 126, with the spring constant cl. In this model, the following values are obtained for the constants, in the summing member 120
C1 = - k2: m2
C2 = - k2: m2
This model starts from the principle of constant damping of the superstructure and neglects the damping of the suspension movement of the tires. However, a surprisingly good correspondence of the real values of the vertical acceleration (dotted line 130 in FIG. 6) with the values determined according to the present invention (continuous curve 132) has appeared.

Claims (6)

 1. Method for determining an acceleration of the vehicle superstructure of a vehicle comprising hydraulic or hydropneumatic components (16; 50), for the transmission of forces between the chassis and the vehicle body, characterized in this flood, l '' the fluid pressure (Pa) momentarily prevailing in the component under consideration (16; 50) is measured, and a vehicle acceleration value (z2 is deduced from the measured fluid pressure (Pa) ).  2. Method according to claim 1, characterized in that one determines the parallel component of the acceleration of the superstructure of the vehicle, parallel to the direction of transmission of the forces of the component considered, in that one subtracts from the value of measured fluid pressure (Pa), a constant average pressure value (Po), to form a dynamic pressure value (P), and in that the dynamic pressure value (P) is multiplied by a factor predetermined (C) depending on the design of the chassis, to form the parallel component (z2).  3. Method according to claim 1 or 2, characterized in that, in the case of a component (50) of the type of a cylinder-piston rod unit, with connection channel (68; 70) having a point d 'throttle (D) can be regulated if necessary, between the two interior cylinder spaces (58, 60) separated from each other by the piston (56), the instantaneous pressure (Pa) of the component is used the difference in fluid pressures (P1, P2), weighted correspondingly to the active piston surfaces (A1, A2).  4. Device for implementing the method according to any one of the preceding claims, comprising  - at least one fluid pressure sensor (24; 76; 78), for measuring the pressure of the fluid (Pa) in a hydraulic or hydropneumatic component (18; 50) for transmitting forces between the chassis (12) and the bodywork (11),  a subtraction member (30) for determining a dynamic pressure value (P) by subtracting an average pressure value (Po) from the measured fluid pressure value (Pa), and,  - a multiplier (34) for determining a parallel component (z 2) of the acceleration of the vehicle superstructure, parallel to the direction of the transmission of forces of the body in question, by multiplying the dynamic pressure value (P) by a predetermined factor (C).  5. Method for determining an acceleration of a vehicle superstructure comprising a displacement sensor (110) for determining the difference (zrel) between a part of the chassis and the bodywork, particularly according to any one of claims 1 to 3 , characterized in that an instantaneous speed value (zrel) is deduced from the instantaneous spacing value (zrel) measured each time by differentiation as a function of time, and that an acceleration value is determined of the superstructure by forming the weighted sum of the instantaneous spacing value (zrel) and the instantaneous speed value (zrel) according to predetermined weighting factors (C1, C2).  6. Device for implementing the method according to claim 5, comprising  - a displacement sensor (110) to determine the difference (zrel) between a part of the chassis and the bodywork,  a differentiation member (118) as a function of time, for the measured instantaneous spacing value (zrel), to form an instantaneous speed value (zrel) and,  - a summing member, to form a weighted sum of the instantaneous spacing value (zrel) and the instantaneous speed value (z5rel).