Control of a suspension system of a vehicle provided with four semi-active suspensions

A method for controlling four semi-active suspensions of a vehicle comprising the steps of: determining, for each semi-active suspension, a first and a second signal representative of the acceleration and speed of the sprung mass; determining, for a pair of semi-active suspensions arranged on one side of the vehicle a third and a four signal representative of the acceleration and pitch speed; calculating for each semi-active suspension, a first damping coefficient as a function of the difference between the first and second signal squared; calculating for each semi-active suspension, a second damping coefficient as a function of the difference between the third and the four signal squared; for each semi-active suspension, comparing the first and the second damping coefficient for determining the higher coefficient; applying to each force generator device, an electronic control signal indicative of the respective high damping coefficient.

TECHNICAL SECTOR OF THE INVENTION

The present invention relates to a control of a suspension system of a vehicle provided with four semi-active suspensions. In particular, the present invention relates to an independent control of four controllable force generators comprised in four respective semi-active suspensions of a suspension system mounted on a four-wheel vehicle, in particular a motor vehicle, to which explicit reference will be made in the following description without therefore loosing in generality.

STATE OF THE ART

As known, latest-generation vehicles are provided with a suspension system having the function of damping the oscillatory motion of the vehicle so as to reduce oscillations, pitch and heave of the same, to ensure, on one hand, ride comfort of the passengers aboard the vehicle as the roughness of the terrain varies and, on the other hand, to guarantee handling as the contact force between tire and road surface varies.

In particular, latest-generation suspension systems essentially comprise four suspensions of semi-active type, each of which is interposed between the body or chassis of the vehicle, herein indicated as “sprung mass” and a respective wheel of the vehicle, indicated hereinafter as “unsprung mass”. It is worth specifying that the unsprung mass, comprises, in addition to the rim and to the tire which compose a wheel, also the braking system and the motion transmission members associated to the wheel itself.

Each semi-active suspensions typically comprises a spring, characterized by a predetermined elastic constant interposed between the sprung mass and the unsprung mass; and a force generator device or shock absorber, which interconnects the sprung mass to the unsprung mass.

The force generator device is structured so as to adjust the damping force exerted between the sprung mass and the unsprung mass, as a function of an electric control signal generated by an electronic control system.

In particular, the electronic control system comprises measuring system which determines some predetermined physical quantities, such as, for example, the speed of the unsprung mass or by the sprung mass along a vertical direction and/or the vertical acceleration induced on the semi-active suspension when the vehicle runs on a road profile; and an electronic control device, which generates the control signal to be imparted to each force generator device, on the basis of a determined damping law applied to the determined physical quantities.

The measuring system essentially contemplates at least one accelerometer installed on the sprung mass and/or on the unsprung mass at each vehicle suspension.

In the case in point, international application WO 2008/010075, filed by “Politecnico di Milano”, describes a method for controlling a force generator comprised in a semi-active suspension, wherein it is contemplated to essentially discriminate a dominating energizing frequency on the basis of the measured vertical acceleration of the suspension; and to select the damping coefficient to be controlled by the semi-active suspension, by means of the force generator, on the basis of the calculated dominating vertical energizing frequency.

In particular, the method described in the aforementioned international application essentially contemplates detecting a first signal representative of the sprung mass acceleration; detecting a second signal representative of the sprung mass speed; determining a value of the difference between the first signal squared and the second signal squared; and applying to the force generator a control signal as a function of the value of the difference between the first and the second signal squared so as to determine whether the semi-active suspension has high or low frequency vertical dynamics.

In the case in point, the method described in the aforementioned international application assigns to the damping coefficient used by the force generator a predetermined minimum value or a maximum value on the basis of the frequency of high or low frequency vertical dynamics.

The aforesaid method completely disregards the entity of the energizing determined by the road profile, but only considers the stress frequency that it implies on the sprung mass of the vehicle. Therefore, by implementing the method described above, it may occur that low frequency events which are not very relevant in energy terms determine the selection of the maximum predetermined value, causing a maximum damping, and introducing, as a consequence, undesired vibrations with negative repercussions on comfort aboard the vehicle. In other words, the aforementioned method contemplates selecting an alternative maximum or minimum damping coefficient on the basis of the body dynamics. It may consequently occur that the method determines the instantaneous selection of maximum damping when instead a continuous transition would be more effective in terms of comfort.

Furthermore, the application of the solution described in the international application published under number WO 2008/010075 on a four-wheel vehicle necessarily contemplates using four accelerometers each associated to a corresponding semi-active suspension.

OBJECT AND SUMMARY OF THE INVENTION

The applicant has conducted an in-depth study with the objective of identifying a solution which specifically allows to reach the following objectives:reduce the number of accelerometers needed for controlling four semi-active suspensions present in a four-wheel vehicle so as to reduce the overall manufacturing cost of the system, on one hand, and on the other to simplify the same in terms of wiring, wire fastening system, brackets etc.;to improve comfort onboard also when the semi-active suspensions are subject to low frequency events which are not very relevant in terms of energy.

It is thus the object of the present invention to make a solution available which allows to reach the objectives indicated above.

This object is reached by the present invention because it relates to a device and a method for controlling the vertical dynamics of a vehicle provided with four semi-active suspensions, as defined in the attached claims.

The present invention will now be described in detail with reference to the appended figures to allow a person skilled in the art to make it and use it. Various changes to the described embodiments will be immediately apparent to people skilled in the art, and the described generic principles may be applied to other embodiments and applications without because of this departing from the scope of protection of the present invention, as defined in the appended claims. Therefore, the present invention must not be considered limited to the described and illustrated embodiments but instead confers the broadest scope of protection, in accordance with the principles and features described and disclosed herein.

FIG. 1diagrammatically shows by way of non-limiting example, a vehicle1, such as, for example, motor vehicle comprising a body/chassis2, indicated hereinafter as sprung mass Ms, four resting wheels3of the vehicle on the ground (indicated hereinafter as road profile R), each of which will be indicated hereinafter as unsprung mass Ns, and a suspension system4having the function of damping the oscillatory movement of the vehicle1to reduce pitch and/or heaving.

The suspension system4comprises four semi-active suspensions5associated to the wheels3, thus arranged at the four angles2a,2b,2cand2dof the body/chassis2of the vehicle1i.e. at the ends of the front and rear axles of the vehicle1, and are interposed between the sprung mass Ms and the unsprung mass Ns in known manner and thus not described in detail.

Each semi-active suspension5is structured so as to adjust the damping force exerted between sprung mass Ms and unsprung mass Ns according to an electric control signal Sci (i comprised between 1 and 4) associated to a damping coefficient CiT(t) calculated in the manner described in detail below.

With reference to the diagrammatically example shown inFIG. 2, each semi-active suspension5comprises a mechanical elastic member, preferably a spring6, having a predetermined elastic constant k, which is interposed between the sprung mass Ms and the unsprung mass Ns; and a controllable damper, hereinafter indicated as force generator device7, which is structured so as to adjust the damping force between the sprung mass Ms and the unsprung mass Ns of the vehicle1, as a function of the electric control signal Sci, so as to control the vertical dynamics of the unsprung mass Ns.

The suspension system4is further provided with an electronic control system8comprising a measuring system9, which is adapted to measure a series of physical quantities introduced by the road profile R on the three semi-active suspension5of the vehicle1, such as, for example, vertical acceleration, {umlaut over (z)} of the sprung mass Ms and/or the speed ż of the sprung mass Ms along a vertical direction.

With reference to a preferred embodiment shown inFIGS. 1 and 2, the measuring system9comprises three acceleration sensors10, such as, for example, accelerometers, which are arranged on the sprung masses Ms present in the three angles2a,2band2cof the vehicle1, respectively, which, in the illustrated example, correspond to the two front angles2a2bof the vehicle1, and to a rear angle2cof the vehicle1, and are adapted to generate three measuring signals associated to the measured vertical accelerations.

It is however worth specifying that the arrangement of the acceleration sensors10in the three angles of the vehicle1shown inFIG. 1must not be considered limiting because the acceleration sensors10may be distributed in the angles themselves according to any arrangement, also different from that shown.

With reference to the preferred embodiment shown inFIG. 2, the electronic control system8further comprises a processing/control unit11, which is configured for:receiving in input the three measuring signals representative of the three vertical accelerations {umlaut over (z)}1, {umlaut over (z)}2, {umlaut over (z)}3of the sprung masses Ms1, Ms2and Ms3associated to the angles2a,2band2cand measured by the respective acceleration sensors10;processing the three accelerations {umlaut over (z)}1, {umlaut over (z)}2, {umlaut over (z)}3so as to estimate the acceleration {umlaut over (z)}4of the sprung mass Ms4associated to the fourth angle2d, free from acceleration sensor;processing the three measured accelerations {umlaut over (z)}1, {umlaut over (z)}2, {umlaut over (z)}3ad the estimated acceleration {umlaut over (z)}4for calculating the first damping coefficients cHi(i comprised between 1 and 4) adapted to be set on the semi-active suspensions5by means of a control of the force generator device7, to minimize the vertical acceleration variance, i.e. the vertical dynamics of each semi-active suspension5;processing two of the four accelerations, e.g. accelerations {umlaut over (z)}1and {umlaut over (z)}3, associated to two sprung masses Ms1and Ms3arranged in two respective angles, e.g. the angles2aand2c, arranged on the same side Dx or Sx (right side or left side, parallel to the longitudinal axis L of the vehicle1shown inFIG. 1), so as to determine second damping coefficients cPi(i comprised between 1 and 4) to be set on, the semi-active suspensions5by means of the force generator control7to minimize the pitch dynamics of the vehicle1;comparing each first damping coefficient cHiwith the second damping coefficient cPieach associated to the same angle, so as to determine the higher damping coefficient CTi=MAX(cHi,cPi) between the two, and to generate for each semi-active suspension5the electric control signal Sci indicative of the higher damping coefficient CTito be set on the semi-active suspension5present in the angle itself by means of the force generator device7.

With reference toFIG. 2, the processing/control unit11essentially comprises an acceleration estimate module12, a first control module13, a second control module14, and a supervisor module15.

The acceleration estimate module12is configured to estimate the acceleration along a vertical direction of the sprung mass Ms associated to the fourth angle2dof the vehicle1free from accelerator sensor.

In the embodiment shown inFIGS. 2 and 3, the acceleration estimate module12is shaped so as to receive in input the three measuring signal indicative of the three vertical associations {umlaut over (z)}1, {umlaut over (z)}2, {umlaut over (z)}3of the sprung masses Ms1, Ms2and Ms3associated to the measured angles2a,2band2cof the respective acceleration sensors10.

The acceleration estimate module12is further configured to process the three accelerations {umlaut over (z)}1, {umlaut over (z)}2, {umlaut over (z)}3so as to estimate the acceleration {umlaut over (z)}4of the sprung mass Ms4associated to the fourth angle2d, free from acceleration sensor, according to an estimate law associated to a predetermined rigid conduction of the chassis2in a given frequency band of interest for controlling the vertical dynamics.

In the embodiment shown inFIG. 3, the estimate law associated to a predetermined rigidity condition of the chassis2, when executed by the acceleration module12, determines the acceleration {umlaut over (z)}4by means of the following equation:
{umlaut over (z)}4=β1{umlaut over (z)}1+β2{umlaut over (z)}2+β3{umlaut over (z)}3[1]

where β1, β2and β3are predetermined coefficients associated to the respective accelerations and determined by the predetermine rigidity condition of the chassis, to minimize the acceleration {umlaut over (z)}4.

With reference to the embodiment shown inFIGS. 4 and 7, the first control module13is configured so as to determine the first damping coefficients cHito be set on the corresponding force generator devices7so as to control the vertical dynamics of the sprung masses Msi in decentralized manner.

The first control module13is configured for: receiving in input the three measured accelerations {umlaut over (z)}1, {umlaut over (z)}2, {umlaut over (z)}3and the estimated acceleration {umlaut over (z)}4; determining the vertical speeds ż1, ż2, ż3, ż4associated to the respective sprung masses Ms1, Ms2, Ms3and Ms4, as a function of the accelerations {umlaut over (z)}1, {umlaut over (z)}2, {umlaut over (z)}3, {umlaut over (z)}4; determining each of the first damping coefficients cH1, cH2, cH3, and cH4according to the following calculation law:
Si(t)={umlaut over (z)}i2(t)−αi2żi2(t)
c(t)i=fi(Si(t))  [2]

żi(t) is the speed expressed in m/s of the i-th sprung mass Msi determined in instant t;

{umlaut over (z)}i(t) is the acceleration expressed in m/s2of the i-th sprung mass Msi determined in instant t;

αiis the first value indicative of the invariance frequency or cross-over frequency expressed in radians/second; in particular, the cross-over frequency is indicative of the so-called “dominating energizing frequency” to which the i-th sprung mass Msi is subjected, and comprises an intermediate predetermined value which is, on one hand, higher than the frequencies of the low energizing frequency set at of the i-th sprung mass Msi and, on the other hand, lower than the frequencies of the high energizing frequencies set of the i-th sprung mass Msi; αi is preferably a fixed parameter determined beforehand during a step of designing of the i-th semi-active suspension5;

Si(t) is s a first function with provides a second value indicative of the frequency of the energizing energy to which the i-th sprung mass is subjected in instant t; in particular, the negative sign Si(t) is indicative/associated to a low band; the positive sign Si(t) is indicative/associated to the high band; while the width of Si(t) is associated to a measure of the energy quantitative; and

fi(Si(t)) is a second function providing a third value which is indicative of the variance of the first damping coefficient cHito be set on the force generator7of the i-th semi-active suspension5, as the second value Si(t) indicative of the frequency and energizing energy to which the i-th sprung mass is subjected in instant t. In other words, the second function fi(Si(t)) is a function which is indicative of the variance of the first damping coefficient CHias the energizing frequency to which the i-th sprung weight is subjected in instant t varies.

From the above, it is worth specifying that the second function fi(Si(t)) differs from the first and second control law described in the aforesaid international patent application WO 2008/010075 because the latter are both based on a continuous step function comprising a maximum damping value and a minimum damping value both constant as the frequency varies and associated to the high and low energizing frequencies. In particular, the maximum value of the discontinuous function, described in international patent application WO2008010075, is associated to a constant maximum damping coefficient c(t)=cmaxand is provided by the discontinuous function when S(t)<0, i.e. when the energizing frequency of the sprung mass, determined by means of the function S(t), is lower than the cross-over frequency, while the second value associated to a minimum predetermined damping coefficient c(t)=cminis provided by the discontinuous function when S(t)>=0 when the energizing frequency is higher than the cross-over frequency. Thus the first and second law contemplate a behavior similar to that of a frequency selector, which “switches” the damping coefficient to be set to the force generator device7between a maximum and a minimum value predetermined as a function of the determined high/low energizing frequency. The method described in the aforementioned international application WO 2008/010075 is thus limited to considering only the energizing/stress frequency that the road causes on the sprung mass to the vehicle but does not consider the energy, i.e. the energy associated to the energizing caused on the mass itself when subjected to a given energizing frequency. It thus occurs that events which are not very relevant in energy terms, i.e. having a low intensity/energy characterized by a low frequency, determine the switching of the selector which selects the maximum damping coefficient, causing undesired vibrations with negative repressions on comfort aboard the vehicle. Thus, the control method of the suspension described in international application n. WO2008010075 is based exclusively on the information related to the sign of the selector in frequency S(t).

However, studies carried out by the applicant have demonstrated that the value of the module of the value obtained by means of the frequency selector S(t) contains useful information related to the energizing energy, which is bound in terms of quadratic acceleration and vertical speed of the sprung mass Ms. In light of this study, the applicant has identified a method which conveniently determines by means of the selecting function S(t) not only the value correlated to the energizing frequency of the sprung mass Ms, but also a value which is indicative of the energizing energy in instant t caused on the sprung mass by the road profile run by the vehicle1.

FIG. 5shows a set of experimental values of the road energizing energy measured/determined by the applicant by implementing a first function Si(t) described below, in which it is possible to note that the module of the value obtained by the first function Si(t) itself, i.e. the energizing energy, is subjected to particularly significant instantaneous reduction when the road run by the vehicle passes from a rough pattern (English track) to a flat-smooth pattern (fast ring).

FIG. 6instead shows a possible embodiment of the second function fi(Si(t)) associated to the i-th semi-active suspension5.

The second function fi(Si(t)) is representative of a

Cartesian diagram in which the abscissa axis shows the energizing frequency calculated by means of the first function, i.e. the value of the measure provided by Si(t), while the ordinate axis shows the variation of the first damping coefficient cHias the energizing frequency varies.

In particular, in the embodiment shown inFIG. 6, the second function fi(Si(t)) is characterized by:a Dead-Zone—DZ associated to an energizing frequency band deemed irrelevant for vertical dynamics, in which the second function fi(Si(t)) has a first constant damping coefficient cHiequal to cfixed;—High-Frequency-Zone—HFZ associated to a high frequency energizing band, and representative inFIG. 6by a segment which passes through points HF1and HF2(associated to one of the experimental values), and indicates the variation of the first damping coefficient cHiin the high frequency band;a Low-Frequency/Low-Energy-Zone—LFLEZ associated to a low entity energizing energy variation in a low frequency energizing frequency band, represented inFIG. 6by a segment which passes through points LE1, LE2and LE3and indicates the variation of the first damping coefficient cHiin the “low frequency/low-energy-zone” band;a Low-Frequency/High-Energy-Zone—LFHEZ associated to a high entity energizing energy variation in a low frequency energizing frequency band, represented inFIG. 6by a segment which passes through points HE1, HE2and HE3and indicates the variation of the first damping coefficient cHiin the “low frequency/high-energy-zone” band.

With regards to the above, it is worth underlining that the trend of the second function fi(Si(t)) shown inFIG. 6was established in order to approximate in “smooth” manner the discontinuous function S(t) described in the aforementioned international application WO 2008/010075 and shown inFIG. 6with F(MIX-1), so as to obtain, in use, a gradual damping in case of low frequency events, and thus avoid excessively high stiffening which could give rise to annoying vibrations perceivable by the passengers of the vehicle1.

With reference toFIGS. 4 and 7, the first control module13comprises four heave calculation blocks MIX-Ci(i comprised between 1 and 4), each of which is associated to a semi-active suspension5and is adapted to receive in input the acceleration {umlaut over (z)}i(t) associated to the i-th suspended mass Msiand outputs the first damping coefficient cHito be set on the force generator device from7of the i-th semi-active suspension5.

According to a preferred embodiment shown inFIG. 7, each heave calculation block MIX-Cicomprises: an integration device18which receives in input the acceleration {umlaut over (z)}i(t) and integrates over time the acceleration {umlaut over (z)}i(t) so as to output a value indicative of the speed żi(t) of the sprung mass Msi.

Each heave calculation block MIX-Cifurther comprises a multiplier device19, which receives in input the speed żi(t); and multiplies the speed żi(t) for the cross-over αifrequency; a squarer device20, which receives in input the value αi·żi(t) and squares it so as to output the value (αi·żi(t))2; a squarer device21, which receives in input the acceleration {umlaut over (z)}i(t) and squares it so to output ({umlaut over (z)}i(t))2; a adder node22, which receives in input the acceleration squared ({umlaut over (z)}i(t)) and the value (αi·żi(t))2and calculates the difference between acceleration squared ({umlaut over (z)}i(t))2and the value (αi·żi(t))2so as to provide the second value S(t).

Each heave calculation block MIX-Cifinally comprises a control block23, which receives in input the second value Si(t), which is indicative of the energizing frequency of the i-th sprung mass Msi and determines by means of the second function fi(Si(t)) the third value, which is indicative of the variation of the first damping coefficient cHito be set on the force generator7of the i-th semi-active suspension5, as the second value indicative of the energizing frequency to which the i-th sprung mass Msi is subjected in instant t.

With reference toFIGS. 2 and 8, the second control module14is essentially based on an application of the calculation law [2] described above in detail, at the pitch motion of the vehicle1, instead of the vertical motion described above.

It is indeed possible to process two of the four accelerations which in the illustrated example corresponds to the accelerations {umlaut over (z)}1and {umlaut over (z)}3, associated to the two sprung masses Ms1and Ms3arranged in two respective angles, e.g. the angles2aand2c, arranged on the same right hand Dx or left-hand SX side, so as to determine the second damping coefficients cPi(i comprised between 1 and 4) to be imposed to the semi-active suspensions5by controlling the force generator7for minimizing the dynamics associated to the pitch of the vehicle1.

In particular, the pitch acceleration is correlated to the difference between the accelerations {umlaut over (z)}1and {umlaut over (z)}3associated to two sprung masses Ms1and Ms3.

According to a preferred embodiment, the second control module14calculates the second damping coefficients cPiby means of the following calculation law:
{umlaut over (θ)}(t)={umlaut over (z)}1(t)−{umlaut over (z)}3(t)
Sθ(t)={umlaut over (θ)}2(t)−(αθ{dot over (θ)}(t))2
C1p(t)=C2P(t)=ffront(Sθ(t))
C3P(t)=C4P(t)=frear(Sθ(t))  [3]

{umlaut over (θ)}(t) is the pitch acceleration of the vehicle in instant t expressed in m/s2;

{dot over (θ)}(t) is the pitch speed of the vehicle in instant t expressed in m/s;

αθis the first value indicative of the invariance frequency or cross-over frequency expressed in radians/second for the pitch motion of the vehicle;

Sθ(t) is a third function which provides a second value indicative of the frequency of the energizing energy to which the i-th sprung mass is subjected in instant t caused by the pitch dynamics;

ffront(Sθ(t)) is a fourth function providing a third value which is indicative of the variance of the two second damping coefficients Cip(t) e C2p(t) to be set on the force generators7of the respective semi-active suspensions5arranged in angles2aand2bpresent on the front side of the vehicle; and

frear(Sθ(t)) is a fourth function providing a third value which is indicative of the variance of the two second damping coefficients C3p(t) e C4p(t) to be set on the force generators7of the respective semi-active suspensions5arranged in the angles2cand2dpresent on the rear side of the vehicle.

With reference toFIGS. 4 and 8, the second control module14comprises: an adder node16, which receives in input the accelerations {umlaut over (z)}1and {umlaut over (z)}3associated to two sprung masses Ms1and Ms3, and determines the difference between the accelerations {umlaut over (z)}1(t) and {umlaut over (z)}3(t) so as to calculate the pitch acceleration {umlaut over (θ)}(t); an integration device24, which receives input the pitch acceleration {umlaut over (θ)}(t) and integrates it over time so as to calculate the pitch speed {dot over (θ)}(t); a multiplier device25, which revives in input the pitch speed {dot over (θ)}(t) and multipliers by a first value indicative of the invariance frequency or cross-over frequency so as to obtain the value (αθ{dot over (θ)}(t)); a squarer device26which receives in input the value (αθ0{dot over (θ)}(t)) and squares it so as to obtain the value (αθ{dot over (θ)}(t))2; a squarer device27, which receives in input the pitch acceleration {umlaut over (θ)}(t) so as to square it {umlaut over (θ)}(t)2; an adder node28, which receives in input the pitch acceleration {umlaut over (θ)}(t)2and the value (αθ{dot over (θ)}(t))2and calculates the difference {umlaut over (θ)}2(t)−(αθ{dot over (θ)}(t))2so as to determine the second value Sθ(t) indicative of the energizing energy.

With reference toFIGS. 4 and 8, the second control module14further comprises a second control block29which receives in input the second value Sθ(t) and implements the fourth function ffront(Sθ(t)) so as to output the third value which is indicative of the variation of the two second damping coefficients C1p(t) e C2p(t) to be set on the force generators7of the respective semi-active suspensions5arranged in the angles2aand2bpresent on the first side of the vehicle1.

The second control module14further comprises a second control block30which receives in input the second value Sθ(t) and implements the fourth function frear(S74(t)) so as to output the third value which is indicative of the variation of the two second damping coefficients C3p(t) and C4p(t) to be set on the force generators7of the respective semi-active suspensions5arranged in the angles2cand2dpresent on the first side of the vehicle1.

The supervisor module15is configured to generate the damping reference for each angle of the vehicle1by comparing the first damping coefficients cHiassociated to the vertical dynamics of each semi-active suspension5generated by the first control module13with the second damping coefficients cPigenerated by the second control module14.

The supervisor module15is configured so as to privilege damping/contrast of low frequency, high energy dynamics, the most perceivable by passengers. Thus supervision is carried out by selecting for each angle of the vehicle the higher damping requested by either the first13or the second control module14.

In particular, the supervisor module15is configured so as to receive in input the first and second damping coefficients and cHiand cPigenerated by the first13and, respectively, by the second control module14; determining the higher damping coefficient CTi=MAX(cHi, cPi) between the two and generated for each semi-active suspension5the electric control system Sci which is indicative of the higher damping coefficient CTito be set to the semi-active suspension5present in the angle itself, by means of the force generator device7.

In the embodiment shown inFIG. 9, the supervisor module15comprises four comparison device31, each of which is associated to a corresponding semi-active suspension5and is configured for: receiving in input the first and the second damping coefficient cHiand cPi; comparing the first and the second damping coefficient cHiand cPiso as to determine the higher damping coefficient CTi=MAX(cHi, cPi); providing the electric control signal Sci(CTi) to the force generator device7associated to the semi-active suspension5itself.

The control method of the semi-active suspensions5provided according to the dictates of the present invention thus contemplates:receiving in input the three measuring signals representative of the three vertical accelerations {umlaut over (z)}1, {umlaut over (z)}2, {umlaut over (z)}3of the sprung masses Ms1, Ms2and Ms3associated to the angles2a,2band2cand measured by the respective acceleration sensors10;processing the three accelerations {umlaut over (z)}1, {umlaut over (z)}2, {umlaut over (z)}3so as to estimate the acceleration {umlaut over (z)}4of the sprung mass Ms4associated to the fourth angle2d, free from acceleration sensor;processing the three measured accelerations {umlaut over (z)}1, {umlaut over (z)}2, {umlaut over (z)}3and the estimated acceleration {umlaut over (z)}4for calculating the first damping coefficients cHi(i comprised between 1 and 4) adapted to be set on the semi-active suspensions5by means of a control of the force generator device7, to minimizes the variance of the vertical acceleration, i.e. the vertical dynamics of each semi-active suspension5;processing two of the four accelerations, e.g. accelerations {umlaut over (z)}1and {umlaut over (z)}3, associated to two sprung masses Ms1and Ms3arranged in two respective angles, e.g. the angles2aand2c, arranged on the same side (right side or left side, opposite with respect to the middle line of the vehicle1), so as to determine second damping coefficients cPi(i comprised between 1 and 4) to be set on the semi-active suspensions5by means of the force generator control7to minimize the pitch dynamics of the vehicle1;comparing each first damping coefficient cHiwith the second damping coefficient cPieach associated to the same angle, so as to determine the higher damping coefficient CTi=MAX(cHi,cPi) between the two, and to generated for each semi-active suspension5the electric control signal Sci indicative of the higher damping coefficient CTito be set on the semi-active suspension5present in the angle itself by means of the force generator device7.

The present invention is advantageous because it allows to use only three accelerometers for controlling the four semi-active suspensions, determining in this manner, on one hand, a reduction of the overall manufacturing costs of the system and obtaining, on the other, a simplification of the same in terms of wiring, wire fastening systems, brackets etc.

Furthermore, by virtue of the calculation of the damping coefficient to the imparted to the force generator based on energizing frequency and entity, it is possible to increase the comfort perceived by passengers in case of events which are not very relevant in energy terms, i.e. in case of vehicle stresses having low intensity/energy characterized by a low frequency.

Finally, the method allows to explicitly control pitch dynamics and consequently better results can be obtained also for this type of dynamics.

It is finally apparent that changes and variations can be made to that described and illustrated without departing from the scope of protection of the accompanying claims.