Patent Description:
The invention relates to a method to control a road vehicle with an active shock absorber.

The movement of passive shock absorbers is entirely determined by the stresses transmitted by the road surface and, therefore, passive shock absorbers are "at the mercy" of the road surface. For a few years now, active shock absorbers have been offered, which are capable of making autonomous movements (namely, completely independent of the stresses transmitted by the road surface), which are added to the movements caused by the stresses transmitted by the road surface; the aim of the autonomous movements made by an active shock absorber is that of reacting to the stresses transmitted by the road surface so as to maximize the dynamic performance of the road vehicle or improve the driving comfort of the road vehicle (the same road vehicle can have its active shock absorbers pursue different targets depending on the type of driving chosen by the driver).

An active shock absorber is provided with a hydraulic or electric shock absorber of its own, which can be controlled so as to generate an autonomous movement (namely, completely independent of the stresses transmitted by the road surface).

Patent application <CIT> discloses a method to control the active shock absorbers of acar and a method to control a road vehicle according to the preamble of claim <NUM>.

The object of the invention is to provide a method to control a road vehicle with an active shock absorber, which is capable of optimizing the damping response.

According to the invention, there is provided a method to control a road vehicle according to the appended claims.

The appended claims describe preferred embodiments of the invention and form an integral part of the description.

In <FIG>, reference number <NUM> indicates, as a whole, a road vehicle provided with two front wheels <NUM> and with two rear wheels <NUM>.

The road vehicle <NUM> is provided with a powertrain system (which is known and is not shown herein), which can comprise an internal combustion engine and/or one or more electric motors and can transmit a motion to the front wheels <NUM> and/or to the rear wheels <NUM>.

A hub <NUM> (schematically shown in <FIG>) of each wheel <NUM> is connected to a frame <NUM> of the road vehicle <NUM> by means of a suspension <NUM> (partially shown in <FIG>), which is provided with an (electronically controlled) active shock absorber <NUM>, which is capable of making autonomous movements (namely, completely independent of the stresses transmitted by the road surface), which are added to the movements caused by the stresses transmitted by the road surface.

According to <FIG>, each active shock absorber <NUM> comprises an element <NUM>, which defines an end of the active shock absorber <NUM>, and an element <NUM>, which defines the other end of the active shock absorber <NUM> and is mounted so as to slide relative to the element <NUM> in order to be able to linearly translate relative to the element <NUM>. Each active shock absorber <NUM> comprises a spring <NUM>, which is connected between the two elements <NUM> and <NUM> and is compressed or expanded when the two elements <NUM> and <NUM> linearly translate relative to one another. Finally, each active shock absorber <NUM> comprises an electric actuator <NUM> (typically, a rotary electric motor), which is configured to have the active shock absorber <NUM> make autonomous movements (namely, completely independent of the stresses transmitted by the road surface) between the elements <NUM> and <NUM>, namely is capable of generating a force F, which is applied between the elements <NUM> and <NUM>. By way of example, the active shock absorbers <NUM> could be of the type described in patent applications <CIT> and <CIT>.

Each active shock absorber <NUM> comprises a position sensor <NUM> (for example, a potentiometer), which provides the relative position p of the two elements <NUM> and <NUM>, namely the exact measure of how much the element <NUM> is translated relative to the element <NUM>. Furthermore, each active shock absorber <NUM> comprises a position sensor <NUM> (for example, a rotary encoder), which provides the angular position α of the electric actuator <NUM>. The road vehicle <NUM> comprises four vertical accelerometers <NUM>, which are mounted on the hubs <NUM> of the wheels <NUM>, namely are rigidly fixed to the hubs <NUM> of the wheels <NUM> in order to move with the hubs <NUM> of the wheels <NUM> in an integral manner. Each vertical accelerometer <NUM> is configured to measure a vertical acceleration az of the corresponding hub <NUM>.

According to <FIG>, the road vehicle <NUM> comprises a longitudinal accelerometer <NUM> and a transverse accelerometer <NUM>, which are mounted on the frame <NUM>, namely are rigidly fixed to the frame <NUM> in order to move with the frame in an integral manner <NUM>, and are configured to measure a longitudinal acceleration ax and a transverse acceleration ay of the frame <NUM> (namely, of the road vehicle <NUM>), respectively. According to a possible embodiment, the two accelerometers <NUM> and <NUM> could be integrated in one single sensor (for example, a triple-axis accelerometer), which provides both the longitudinal acceleration ax and the transverse acceleration ay.

The road vehicle <NUM> comprises an electronic control unit ("ECU") <NUM>, which, among other things, controls the actuators <NUM> of the active shock absorbers <NUM> in the ways described below; from a physical point of view, the control unit <NUM> can consist of one single device or of several devices, which are separate from one another and communicate through the CAN network of the road vehicle <NUM>. The control unit <NUM> is connected (directly or indirectly through a BUS network of the road vehicle <NUM>) to the position sensors <NUM> and <NUM> and to the accelerometers <NUM>, <NUM> and <NUM>.

According to <FIG>, the control unit <NUM> implements an estimating block <NUM>, which determines (estimates) a speed v of translation between the two elements <NUM> and <NUM> of the active shock absorber <NUM>. According to a preferred embodiment, the estimating block <NUM> estimates the speed v of translation between the two elements <NUM> and <NUM> of the active shock absorber <NUM> based on a moving speed of the actuator <NUM> of the active shock absorber <NUM> (determined by deriving, in the time, the position p of the actuator <NUM> measured by the position sensor <NUM>), based on the relative position p between the two elements <NUM> and <NUM> of the active shock absorber <NUM> (directly measured by the position sensor <NUM>) and based on the vertical acceleration az in the area of the hub <NUM> (directly measured by the vertical accelerometer <NUM>).

According to <FIG>, the control unit <NUM> implements a control block <NUM>, which, by using an open-loop transfer function TF<NUM>, determines a contribution C<NUM> exclusively based on the sole vertical acceleration az in the area of the hub <NUM> (directly measured by the vertical accelerometer <NUM>); in other words, the contribution C<NUM> exclusively depends on the sole vertical acceleration az in the area of the hub <NUM>. Furthermore, the control unit <NUM> implements a control block <NUM>, which, by using an open-loop transfer function TF<NUM>, determines a contribution C<NUM> exclusively based on the sole speed v of translation between the two elements <NUM> and <NUM> of the active shock absorber <NUM> (provided by the estimating block <NUM>); in other words, the contribution C<NUM> exclusively depends on the sole speed v of translation between the two elements <NUM> and <NUM> of the active shock absorber <NUM>. Finally, the control unit <NUM> implements an adder block <NUM>, which calculates the target force FTGT of the actuator <NUM> by only and exclusively adding the two contributions C<NUM> and C<NUM> (it should be pointed out that the two contributions C<NUM> and C<NUM> also have a sign and, therefore, their sum is calculated taking into account the sign) ; namely, the value of the target force FTGT of the actuator <NUM> is exclusively determined by the sum of the sole contributions C<NUM> and C<NUM>.

Basically, the open-loop transfer function TF<NUM> entails the force F generated by the actuator <NUM> (namely, the contribution C<NUM> of the target force FTGT of the actuator <NUM>) being substantially proportional to the speed v of translation between the two elements <NUM> and <NUM> of the active shock absorber <NUM>; namely, it increases as the speed v of translation between the two elements <NUM> and <NUM> of the active shock absorber <NUM> increases. Indeed, the gain of the transfer function TF<NUM> is measured in [Ns/m] as, by being multiplied by the speed v of translation (measured in [m/s]), it directly provides the contribution C<NUM> of the target force FTGT of the actuator <NUM> (measured in [N]).

In other words, the contribution C<NUM> is determined based on the sole vertical acceleration az of the hub <NUM> and using the open-loop transfer function TF<NUM>, which provides the contribution C<NUM> based on the vertical acceleration az; similarly, the contribution C<NUM> is determined based on the sole speed v of translation between the two elements <NUM> and <NUM> of the active shock absorber <NUM> and using the open-loop transfer function TF<NUM>, which provides the contribution C<NUM> based on the speed v of translation. Hence, the control unit <NUM> determines the target force FTGT based on the vertical acceleration az of the hub <NUM> and based on the speed v of translation between the two elements <NUM> and <NUM> of the active shock absorber <NUM> by exclusively using open-loop transfer functions TF<NUM> and TF<NUM>.

Basically, the contribution C<NUM> determined based on the vertical acceleration az constitutes an inertia compensation, whereas the contribution C<NUM> determined based on the speed v of translation between the two elements <NUM> and <NUM> of the active shock absorber <NUM> constitutes a damping compensation.

According to a preferred embodiment, the transfer functions TF<NUM> and TF<NUM> are variable as the frequency varies (generally, ranging from <NUM> to <NUM>) and have a gain and a phase.

To sum up, the control unit <NUM> determines the target force FTGT for the actuator <NUM> of the active shock absorber <NUM> based on the vertical acceleration az of the hub <NUM> (directly measured by the vertical accelerometer <NUM>) and based on the speed v of translation between the two elements <NUM> and <NUM> of the active shock absorber <NUM> (provided by the estimating block <NUM>). The control unit <NUM> controls the actuator <NUM> of the active shock absorber <NUM> so as to pursue the target force FTGT; according to a preferred embodiment, the target force FTGT determined by the control unit <NUM> only and exclusively based on the vertical acceleration az of the hub <NUM> and on the speed v of translation between the two elements <NUM> and <NUM> of the active shock absorber <NUM> could be added to other target forces determined in other ways and so as to pursue other targets (as described, for instance, in <CIT>and <CIT>).

According to a preferred embodiment, the transfer function TF<NUM> consists of a map of experimentally determined points. In particular and according to <FIG>, at first an optimal and desired transfer function TF<NUM>-OPT is established on paper in order to have an optimal and desired damping; subsequently, a measured transfer function TF<NUM>-MSR is experimentally determined by using mechanical stresses of the suspension <NUM> and by always keeping the second contribution C<NUM> at zero, namely by always having the target force FTGT coincide with the sole first contribution C<NUM>. Finally, the transfer function TF<NUM> is determined as difference between the optimal and desired transfer function TF<NUM>-OPT and the measured transfer function TF<NUM>-MSR.

The embodiments described herein can be combined with one another.

The control method described above has different advantages.

First of all, the control method disclosed above optimizes the damping response of the active shock absorber <NUM> (both in terms of effectiveness of the response and in terms of promptness of the response), though maintaining a hood level of comfort.

Furthermore, the control method disclosed above is particularly stable and safe as, by operating in open loop, it never risks triggering undesired oscillations.

Claim 1:
A method to control a road vehicle (<NUM>) comprising;
a frame (<NUM>);
at least one wheel (<NUM>) provided with a hub (<NUM>); and
a suspension (<NUM>), which connects the frame (<NUM>) to the hub (<NUM>) of the wheel (<NUM>) and is provided with an active shock absorber (<NUM>) comprising: a first element (<NUM>), which defines an end of the active shock absorber (<NUM>), a second element (<NUM>), which defines another end of the active shock absorber (<NUM>) and is mounted so as to slide relative to the first element (<NUM>); and an actuator (<NUM>), which is configured to generate a force (F), which is applied between the two elements (<NUM>, <NUM>);
the control method comprises the steps of:
determining a vertical acceleration (az) of the hub (<NUM>) ;
determining a speed (v) of translation between the two elements (<NUM>, <NUM>) of the active shock absorber (<NUM>);
determining a target force (FTGT) for the actuator (<NUM>) of the active shock absorber (<NUM>) based on the vertical acceleration (az) of the hub (<NUM>) and on the speed (v) of translation between the two elements (<NUM>, <NUM>) of the active shock absorber (<NUM>);
controlling the actuator (<NUM>) of the active shock absorber (<NUM>) so as to pursue the target force (FTGT); and
determining a second contribution (C<NUM>) exclusively based on the sole speed (v) of translation between the two elements (<NUM>, <NUM>) of the active shock absorber (<NUM>) and using a second open-loop transfer function (TF<NUM>), which provides the second contribution (C<NUM>) exclusively as a function of the sole translation speed (v);
and
determining a first contribution (C<NUM>) exclusively based on the sole vertical acceleration (az) of the hub (<NUM>) and using a first open-loop transfer function (TF<NUM>), which provides the first contribution (C<NUM>) exclusively as a function of the sole vertical acceleration (az); the control method is characterized in that it comprises the further step of:
calculating the target force (FTGT) by only and exclusively adding the two contributions (C<NUM>, C<NUM>).