Method of adjusting an estimated value of the height of the gravity center of a vehicle
A method for adjusting an estimated height of the center of gravity (HCOG) value of a vehicle includes concomitant calculations, based on parameters dependent on the HCOG value and parameters independent from the HCOG value. The method further comprises the adjustment of a parameter related to the HCOG value.
1. A method for adjusting an estimated HCOG value of a vehicle V, comprising a front axle and a rear axle, said method comprising the steps of:
a) determining the slippage rate (RF) for the wheels of the front axle and the slippage rate (RR) for the wheels of the rear axle during a braking period according to the general formulae:
R
F
=
VS
-
WSF
VS
*
100
(
i
)
R
R
=
VS
-
WSR
VS
*
100
(
ii
)
wherein
(VS) denotes the linear speed of the vehicle (V),
(WSF) denotes the linear speed of the front wheel,
(WSR) denotes the linear speed of the rear wheel,
b) deducing from the slippage rate (RF) and (RR) determined in step a), the reference value (ΔNref) corresponding to the difference between the normal force (NF) applied to the wheels of said front axle and the normal force (NR) applied to the wheels of said rear axle, using parameters independent from the HCOG value, by:
b1) determining the adherence (AF) for the wheels of said front axle, and the adherence (AR) for the wheels of said rear axle, according to at least one pre-established curve linking the slippage rate of a wheel to its adherence,
b2) determining the tangential forces (TF) for the wheels of said front axle and the tangential forces (TR) for the wheels of said rear axle according to the formulae:
TF
=
Q
*
KF
Wrad
(
iii
)
TR
=
Q
*
KR
Wrad
(
iv
)
wherein
(Q) denotes the brake factor,
(KF), and (KR) respectively denote the brake pressure at the front wheels and at the rear wheels,
(Wrad) denotes the radius of the considered wheels (W),
b3) deducing from the steps b1) and b2) the normal force (NF) for the wheels of said front axle, and the normal force (NR) for the wheels of said rear axle according to the formulae:
AF
=
TF
NF
(
v
)
AR
=
TR
NR
(
vi
)
wherein
(AF), (AR), denote the adherence determined in step b1),
(TF), (TR) denote the tangential forces determined in step b2), and
(NF), (NR), respectively denote the normal forces at the front wheels and at the rear wheels,
c) determining the difference (ΔN) between the normal forces applied to the wheels of the front axle and the normal forces applied to the wheels of the rear axle, according to formula:
Δ
N
=
B
*
YG
D
(
vii
)
wherein
(YG) is a variable parameter related to the height of the gravity center of the vehicle,
(D) is the distance separating the front axle and the rear axle, and wherein
(B) denotes the global braking torque applied to the wheels of the vehicle and is defined by formula (5):
B
=
Q
(
KF
+
KR
)
(
viii
)
d) comparing (ΔN) determined in step c) with (ΔNref) determined in step b),
e) adjusting the variable parameter (YG), when necessary, in such a way the difference between (ΔN) and (ΔNref) is below 10%, and
f) adjusting the HCOG value according to (YG) determined in step e), wherein a computing unit provides instructions to a dynamic control system to increase or decrease the HCOG value by a certain amount.
2. The method according to claim 1 , wherein the slippage rates (RF) and (RR) are determined by the means of sensors.
3. A system for adjusting the height of the gravity center of a vehicle comprising a front axle and a rear axle, said system comprising a computing unit (CE), wherein that said computing unit (CE) receives data from one or more sensors (SE) of the vehicle, and a Read Only Memory (ME), wherein said computing unit (CE) is configured to:
a) determine the slippage rate (RF) for the wheels of the front axle and the slippage rate (RR) for the wheels of the rear axle during a braking period according to the general formulae:
RF
=
V
S
-
WSF
VS
*
100
(
i
)
RR
=
V
S
-
W
S
R
V
S
*
100
(
ii
)
wherein
(VS) denotes the linear speed of the vehicle (V),
(WSF) denotes the linear speed of the front wheel,
(WSR) denotes the linear speed of the rear wheel,
b) deduce from the slippage rate (RF) and (RR) determined in step a), the reference value (ΔNref) corresponding to the difference between the normal force (NF) applied to the wheels of said front axle and the normal force (NR) applied to the wheels of said rear axle, using parameters independent from the HCOG value, by:
b1) determining the adherence (AF) for the wheels of said front axle, and the adherence (AR) for the wheels of said rear axle, according to at least one pre-established curve linking the slippage rate of a wheel to its adherence,
b2) determining the tangential forces (TF) for the wheels of said front axle and the tangential forces (TR) for the wheels of said rear axle according to the formulae:
TF
=
Q
*
KF
W
r
a
d
(
iii
)
TR
=
Q
*
K
R
W
r
a
d
(
iv
)
wherein
(Q) denotes the brake factor,
(KF), and (KR) respectively denote the brake pressure at the front wheels and at the rear wheels,
(Wrad) denotes the radius of the considered wheels (W),
b3) deducing from the steps b1) and b2) the normal force (NF) for the wheels of said front axle, and the normal force (NR) for the wheels of said rear axle according to the formulae:
AF
=
TF
NF
(
v
)
AR
=
T
R
N
R
(
vi
)
wherein
(AF), (AR), denote the adherence determined in step b1),
(TF), (TR) denote the tangential forces determined in step b2), and
(NF), (NR), respectively denote the normal forces at the front wheels and at the rear wheels,
c) determine the difference (AN) between the normal forces applied to the wheels of the front axle and the normal forces applied to the wheels of the rear axle, according to formula:
Δ
N
=
B
*
Y
G
D
(
vii
)
wherein
(YG) is a variable parameter related to the height of the gravity center of the vehicle,
(D) is the distance separating the front axle and the rear axle, and wherein
(B) denotes the global braking torque applied to the wheels of the vehicle and is defined by formula:
B
=
Q
(
KF
+
KR
)
(
vii
)
d) compare (ΔN) determined in step c) with (ΔNref) determined in step b),
e) adjusting the variable parameter (YG), when necessary, in such a way the difference between (ΔN) and (ΔNref) is below 10%, and
f) adjust the HCOG value according to (YG) determined in step e), and wherein said computing unit (CE) provides instructions to a dynamic control system to increase or decrease the HCOG value by a certain amount.
4. A vehicle comprising a front axle and a rear axle and equipped with a system for adjusting the height of the gravity center of the vehicle, said system comprising a computing unit (CE), wherein that said computing unit (CE) receives data from one or more sensors (SE) of the vehicle, and a Read Only Memory (ME), wherein said computing unit (CE) is configured to:
a) determine the slippage rate (RF) for the wheels of the front axle and the slippage rate (RR) for the wheels of the rear axle during a braking period according to the general formulae:
RF
=
V
S
-
WSF
V
S
*
100
(
i
)
RR
=
V
S
-
W
S
R
V
S
*
100
(
ii
)
wherein
(VS) denotes the linear speed of the vehicle (V),
(WSF) denotes the linear speed of the front wheel,
(WSR) denotes the linear speed of the rear wheel, b) deduce from the slippage rate (RF) and (RR) determined in step a), the reference value (ΔNref) corresponding to the difference between the normal force (NF) applied to the wheels of said front axle and the normal force (NR) applied to the wheels of said rear axle, using parameters independent from the HCOG value, by:
b1) determining the adherence (AF) for the wheels of said front axle, and the adherence (AR) for the wheels of said rear axle, according to at least one pre-established curve linking the slippage rate of a wheel to its adherence,
b2) determining the tangential forces (TF) for the wheels of said front axle and the tangential forces (TR) for the wheels of said rear axle according to the formulae:
TF
=
Q
*
KF
W
r
a
d
(
iii
)
TR
=
Q
*
K
R
W
r
a
d
(
iv
)
wherein
(Q) denotes the brake factor,
(KF), and (KR) respectively denote the brake pressure at the front wheels and at the rear wheels,
(Wrad) denotes the radius of the considered wheels (W),
b3) deducing from the steps b1) and b2) the normal force (NF) for the wheels of said front axle, and the normal force (NR) for the wheels of said rear axle according to the formulae:
AF
=
TF
NF
(
v
)
AR
=
T
R
N
R
(
vi
)
wherein
(AF), (AR), denote the adherence determined in step b1),
(TF), (TR) denote the tangential forces determined in step b2), and
(NF), (NR), respectively denote the normal forces at the front wheels and at the rear wheels,
c) determine the difference (ΔN) between the normal forces applied to the wheels of the front axle and the normal forces applied to the wheels of the rear axle, according to formula:
Δ
N
=
B
*
Y
G
D
wherein
(YG) is a variable parameter related to the height of the gravity center of the vehicle,
(D) is the distance separating the front axle and the rear axle, and wherein
(B) denotes the global braking torque applied to the wheels of the vehicle and is defined by formula:
B
=
Q
(
KF
+
KR
)
(
viii
)
d) compare (ΔN) determined in step c) with (ΔNref) determined in step b),
e) adjust the variable parameter (YG), when necessary, in such a way the difference between (ΔN) and (ΔNref) is below 10%, and
f) adjust the HCOG value according to (YG) determined in step e), and wherein said computing unit (CE) provides instructions to a dynamic control system to increase or decrease the HCOG value by a certain amount.