Method for estimating the height of the gravity center of a vehicle

1. A method for estimating a height of a gravity center of a vehicle having at least a front axle and a rear axle each carrying at least two wheels, comprising

a) determining a first braking period and a second braking period occurring along road portions having substantially a same slope, but where the first and second braking periods result in different vehicle decelerations, and during both braking periods, estimating at least the following variables:

vehicle acceleration (Acc);

a wheel slippage rate (WSR) for the front and rear axles;

braking forces (Bkf) or braking torque at each of the front and rear axles, or a ratio thereof (K); and

the slope (Slp) of the corresponding road portion;

b) estimating, via one or more electronic control units, using only the estimations of step a) made during both braking periods, the vehicle center of gravity height (H).

2. The method according to claim 1 , wherein the determination that the first braking period and the second braking period result in different vehicle decelerations is achieved by taking into account, during the first braking period and second braking periods, at least one of action of a driver on a brake command device, pressure in a fluidic brake initiating circuit, and acceleration of a wheel.

3. The method according to claim 1 , wherein the slope (Slp) estimation involves determination of an action of forces on the vehicle, of the vehicle mass (M), and of the vehicle acceleration (Acc), and the slope is estimated using the following formula:

Slp

=

Arcsin

(

Acc

-

∑

external

⁢

⁢

forces

M

)

.

4. The method according to claim 3 , wherein, during the first braking period and the second braking period, external forces applied to the vehicle are considered to be limited to the braking threes and to the action of gravity.

5. The method according to claim 4 , wherein the braking forces applied by service brakes of the vehicle are estimated as a function of pressure in fluidic brake initiating circuit(s).

6. The method according to claim 4 , wherein the external forces applied to the vehicle comprise aerodynamic drag of the vehicle.

7. The method according to claim 6 , wherein the aerodynamic drag is estimated as a linear or quadratic function of a speed of the vehicle.

8. The method according to claim 3 , wherein the determination of the vehicle mass (M) comprises the step of comparing vehicle acceleration (Acc) when the vehicle is freewheeling and a vehicle acceleration when the vehicle is accelerating due to provision of a known motoring torque or traction force from a powertrain of the vehicle.

9. The method according to claim 3 , wherein the step of determining vehicle mass (M) is performed during a vehicle acceleration phase involving a gear shift.

10. The method according to claim 1 , wherein the determination of vehicle acceleration (Acc) is performed by derivation of a measured wheel rotation speed (W).

11. The method according to claim 1 , wherein the height of the gravity center of the vehicle is estimated according to the following formula:

H

=

E

·

g

·

cos

⁡

(

slp

)

·

(

WSRf

⁢

⁢

2

WSRf

⁢

⁢

2

+

K

⁢

⁢

2

·

WSRr

⁢

⁢

2

-

WSRf

⁢

⁢

1

WSRf

⁢

⁢

1

+

K

⁢

⁢

1

·

WSRr

⁢

⁢

1

)

Acc

⁢

⁢

2

-

Acc

⁢

⁢

1

where:

H is the estimated height of the gravity center;

E is a distance between front and rear axles;

g is a gravity constant;

Slp is the estimated slope of the road portions on which respective braking periods have been performed; and

K1 and K2 are the estimated values of a front/rear braking ratio, respectively, during the first and second braking periods;

WSRf1, WSRf2 and WSRr1, WSRr2 are front and rear axle wheel speed slippage ratios, respectively, during the first and second braking periods;

Acc1 and Acc2 are the estimated values of the vehicle acceleration Acc, respectively, during the first and second braking periods.